>>81911074No clue; I have never done bare knuckle and I barely talk to anybody else at the gym. I doubt there are many "underground" clubs those seem very rare. Although I would imagine you would not have much trouble finding a guy to fight if you tried. There are plenty of people who just love fighting. At my gym there are certain times where the gym is open without instructors, and you can just go up to somebody and ask if they want to spar. If your gym has that then you should probably ask somebody who goes to those.
If someone I somewhat knew asked me if I wanted to do a bare knuckle fight I would probably do it as long as we got a competent ref.