I know of six clubs, none of which are south of the 57. The closest to you now would be Orange Empire. It now meets in Garden Grove, 4th Saturday of the month (so this Saturday) at 9:00 am at 11832 S. Euclid St., Garden Grove.
The other five clubs are Kofu Kai and Orange County Bonsai, both in Anaheim, the Satsuki Bonsai Club in Santa Ana, and the Vietnamese Bonsai Society in Garden Grove. I've also heard of Hoi Bonsai Viet, but I don't know anything about that club other than it being in the Garden Grove/Westminster area.