How can I quickly stockpile bait for lava fishing?

As of the Terraria Journey’s End update, some fiery critters – namely the Lavafly, Hell Butterfly, and Magma Snail – can spawn in the Underworld. When used as fishing bait, these critters allow one to fish in lava, a very lucrative activity.

Needless to say, gathering these critters is more dangerous than finding regular bait like worms or fireflies, and they also seem to be fairly rare. How can I increase my chances of finding lava bait?