Almost Nothing in SoCal.
There is actually ski shop that specializes in backcountry skis and equipment in San Diego. The shop is called Norpine and has all of the best backcountry ski gear and is a full service shop. The guy who owns and runs the shop is very knowledgeable and all the prices are very reasonable. Right about now, you are probably thinking that it is my shop or a friends or relatives, nope! It is the only shop that I know of down here that has the gear and knows what they are talking about, so as a happy customer, I am simply passing on my recommendation.
He has a pretty good website too.. Norpine.com
Jim (at norpine) can answer any back country ski/boot questions you might have; fit, performance, etc.