There are two main IPSC clubs I know of in SoCal:
at Rahaage's in Norco (off the 10 or 60 fwy), and
SW Pistol League in Piru, between Santa Clarita and Ventura off Hwy 126(?)
SWPL has a good neighboring club, for IDPA shooting, called ISI. Check out
www.isishootists.com I think.