I'm in NY, but there are hella SoCal R3 riders and racers 'round these here parts. A long time R3-forums denizen and Navy dude @Kojiiro just left SD for Japan. He did and/or setup a bunch of rides. Several race at Chuckwalla. Sometimes I wish I was bicoastal so I could ride with the SoCal guys, race at Chuck, and have SoCal weather but I am a NYer to the bone, and if there isn't snow, aren't pot holes, etc it's weird to me.
I used to set up/ride in quite a few non-R3 exclusive rides. I loved doing group rides through SoCals awesome twisties but never got why anyone would want just an R3 specific riding group.
A fellow rider is a fellow rider, whether he is on an R3 or a 14R imo. Get out there and meet the many riders in San Diego, I feel like you are limiting your self if you choose to find an R3 specific group.