This info comes from JohnnyShakes in another recent OC thread. According to yelp this place has Diamond barboxes.
"If you check out Bart's Pub in Garden Grove, they have a pretty nice B/C tournament on Thursday and Sunday nights. $10 entry, 8-ball, race to 1, double elimination. Starts at 9pm. They also have a tournament on Tuesday night that is open to anyone who is rated 13 and under at Hard Times (I think that is the cut off). Same format, and the bar adds $100. You get some pretty strong players there, and if you are looking for action there are probably some people who will accommodate you."