What do you use as a portable lighting mono pole?

A light stand?

As an assistant I have used a light stand with it's legs collapsed in order to hold a strobe with a soft box attached over a location that was difficult to set fixed stands in place. It has the necessary stud/spigot for a strobe built on to it. In fact having the legs on it but collapsed help to keep the pole from rotating due to the weight (gravity) of the soft box, they help to aim the soft box for directing the light to where it is needed.

A boom pole off of a studio light boom.

A Monopod with stud adapter screwed onto the head.

If you are on a budget you can look for used monopods or equipment and get the proper stud/adapter from a photo equip supplier. Maybe an old light stand and remove the legs for a dedicated boom. (I say leave the legs on for control)