Depends on how far people are willing to drive, and put up with players way outside their age group. If I remember right there're folks in Simi, Thousand Oaks, Pasadena, Silverado Cyn, and San Diego. A couple more might be scrapped together out of the Lugola members, and IV was starting up some kind of college BW group in San Diego.
Lugola used to have most of their meetings out in Monrovia, but they've been having them in the OC or vicinity a lot more often lately. You might try organizing something for one of their meetings; that'll provide a safer venue and decrease the opportunities for axe-weilding pedophiles.
Lugola currently does all their organizing through their Yahoo group
, as far as I can tell, so that's the place to start. Even if none of the existing members want to join in the battle themselves, I bet they wouldn't mind playing host to a guest battle.