BMWMC Escondido has a good airhead mechanic, but it is a dealer and in Esco. I don't know anyone in SD that actually goes to the SD dealer.
Dave Campbell services beemers: http://www.dcmwmcservice.com/
I haven't used him for actual work, but he did the estimate on my bike after a crash and missed some important stuff.
There's a bunch of knowledgeable Airheads here that would help you do work yourself if you're so inclined....