Probably the only boxing activities you'll find on campus is groups of beer-chuggers surrounding a TV in a dorm on fight night.
But that's probably not useful to you. I did a quick search and found a couple of boxing gyms in Pomona:
Fist of Gold Boxing, 350 N. Garey Ave., Pomona, CA, 91767
Chuchies Boxing Gym, 700 S Towne Ave, Pomona, CA, 91766-2810
I found these two at this website:
http://www.boxinghelp.com/california.html
Good luck!