Are there hints to the identity of Ivovandas's locus?

I don't see any reason to think we're meant to know

I'm not familiar with the works of Scott Lynch in general, which is why I put this in comments first: in case you'd say that he always puts enough clues in his stories for something like this to be figured out. But since you didn't, and having read this particular story carefully, I don't see why you think there should be any hints about the identity of Ivovandas's locus.

Near the end of the story, Ivovandas says:

I fancy myself fairly adept at identifying the loci in use by my colleagues.

She might be just boasting, but so far she doesn't seem to have claimed any skills or powers that she doesn't have. Perhaps, then, she is particularly expert among magicians in figuring out who's using what locus. To find her own would be an even bigger challenge, suitable perhaps for a gang of particularly skilled thieves, but even they only hope they might figure it out "eventually":

But it’ll give me a good look at everything Amarelle was allowed to see, and that’s much better than nothing. If we can identify her patterns and her habits, the bitch will eventually start painting clues for us as to the location of her own locus.

We saw into Ivovandas's house, through Amarelle's eyes, but I couldn't see any mention of a particular object that she was guarding closely for no apparent reason. She has a tapestry in a cabinet, but that's actually useful, creating maps and contracts: it seems to be a tool rather than a power source.

A comparison with Jarrow doesn't seem to do much good either. Even assuming he lived in or near Prosperity Street, as it seems from the fact that his destruction took place at a "mansion in a private court" around "the north end of Prosperity Street", this doesn't help us to figure out Ivovandas's locus. She lives in High Barrens, her territory empty of other people, but her locus can't be something out and about in the streets there, since she agrees so easily to allow Amarelle's people ("the High Barrens Reclamation Consortium") to go nosing about in the ruins and take what they needed. Since Amarelle didn't tell her the plan, she couldn't know exactly what they were going to do. And she wouldn't trust them to spend long days going around there even if there was a million-to-one chance they'd happen across her locus there - for all she knows, Jarrow might have figured out its location and offered Amarelle a sweeter deal.

“We’re starting a business,” Said Amarelle. “The High Barrens Reclamation Consortium. We need you to sign on as the principal stakeholder.”

“Why?”

“Because nobody can sue you.” Amarelle pulled a packet of paper out of her coat and set them on Ivovandas’ desk. “We need a couple of wagons and about a dozen workers. We’ll provide those. We’re going to excavate wrecked mansions in the High Barrens on days when you and Jarrow aren’t blasting at each other.”

“Again, why?”

“There’s some things we need to take,” said Amarelle with a smile, “and some things we need to hide. If we do it in our names, the heirs of all the families that ran like hell when you settled here and started shooting at other wizards will line up in court to stop us. If you’re the one in charge, they can’t do a damned thing.”

“I will examine these papers,” said Ivovandas. “I will have them returned to you if I deem the arrangement suitable.”

Amarelle found herself on the lawn. But three days later, the papers appeared in her apartments, signed and notarized. The High Barrens Reclamation Consortium went to work.

The only thing in Ivovandas's vicinity that keeps getting mentioned over and over again is her front lawn and the hypnotic toads thereon. That could be again just a tool she uses to torture Amarelle, but if we assume that a locus location is clued in the text of the story, I'd have to guess it's something there.

It wasn’t difficult to find the manse of Ivovandas, the only lit and tended structure in the neighborhood, guarded by smooth walls, glowing ideograms, and rustling red–green hedges with the skeletons of many birds and small animals scattered in their undergrowth. A path of interlocked alabaster stones, gleaming with internal light, led forty curving yards to a golden front door.

Convenient. That guaranteed a security gauntlet.

The screams of terrible flying things high above made concentration even more difficult, but Amarelle applied three decades of experience to the path and was not disappointed. Four trapped stones she avoided by intuition, two by dumb drunken luck. The gravity–orientation reversal was a trick she’d seen before; she cartwheeled (sloppily) over the dangerous patch and the magic pushed her headfirst back to the ground rather than helplessly into the sky. She never even felt the silvery call of the tasteful hypnotic toad sculptures on the lawn, as she was too inebriated to meet their eyes and trigger the effect.

Ivovandas gestured and transported Amarelle to the front lawn of her manse, where the hypnotic toad sculptures nearly cost her even more lost time.

"Mind the hypnotic toads, as I’ve strengthened their enchantments substantially.” She snapped her fingers, and Amarelle was back on the lawn.

“No,” said Ivovandas. Amarelle was returned to the lawn.

_{[this paragraph constitutes a whole chapter just entitled "No", which is also weird]}

However, overall I think we don't know what Ivovandas's locus might be. Unless there's a compelling reason to think we should know, Occam's Razor suggests that information simply isn't hidden in the story.

It's probably not the tavern, but that's not totally unreasonable given what we know

The story is a little vague on the nature of loci, but there are a few things that we can infer.

Jarrow's locus was unusual in it's size

“Forgive me if this is a touchy subject, but I thought the nature of these loci was about the most closely–guarded secret you and your… colleagues possess.”

“Jarrow has been indiscreet,” said Ivovandas. “But then, he understands the knowledge alone is useless if it can’t be coupled to a course of action. A street is quite a thing to dispose of, and the question of how to do so absolutely stymied me until you came calling with your devious head so full of drunken outrage.

This passage implies that Jarrow was less secretive than normal about the nature of his locus because he was less concerned about its destruction than normal. That implies that loci are usually not enormous landmarks (which is why I don't think that the tavern is likely one). Now it could be that the safety of this locus was due to the highly trafficked nature of the street and not it's streetiness itself, but the wording of their discussion makes me think otherwise.

Loci are found, not made

“I wonder how Jarrow figured out it was a locus.” Sophara adjusted the analgesic hat, which had done her much good over the long course of Amarelle’s story. ”I wonder how he harnessed it without anyone interfering!”

This seemingly excludes abstract concepts such as "gold" from being a locus. A specific clump of gold could be a locus perhaps, but not gold in general.

Loci are 'external'
Loci are referred to several times in the text as "external loci". What that means is unclear, but I wouldn't be surprised if a wizard cannot keep it in their possession. The secret of your source of power is not nearly so precious if you can lock the source up in an impenetrable magical vault

It also seems unlikely that the reverse is true and a wizard must keep their locus on their person at all times, since it seems unlikely that Jarrow never left Prosperity Street.

Unfortunately, all this provides very little clue as to what the locus in question actually is.