The Angeles Chapter of the Sierra Club is really good for peak climbing. They have various peak sections, but no training anymore for climbing. They do have a Wilderness Training Committee, but it's the basics and you really might want to advance to rock climbing. They have a number of guides and schools in their newsletter, all private instruction ($$).
There's a guide with plenty of peaks to climb in the Southern CA area, most of them are hikes. You might pick up from the experienced climbers in the Desert and Sierra peak sections, although they are barred from training (insurance). Links on my website.