"Antistatic" Additive

You're going to have to be more specific. If there are contaminants floating around in the air, they are going to stick to the uncured lacquer, regardless of what you add to it.

Typically the fix for this problem is to apply your coating within a spray booth that incorporates a filtration system.

I don't know of an additive for the paint itself. You might try spraying the cured paint with Downey Fabric Softener. That will be temporary at best.

Pink anti-static (ESD) boxes are molded using a soap solution added to the molding compund. I don't know if your PU paint would tolerate some soap, or not. I have no idea how much to recommend if you do try it.

Maybe Mark has an opinion.

If it's cured, a box of drier sheets and an occasional wipe down should help stop static cling.

The ingredients in Static Guard are compatible with some finishes, but again, I think the results would be temporary, if it worked at all.

A simple approach to static reduction is to raise the relative humidity. Sometimes just a room humidifier to keep RH above 50-60% will solve the problem.