Uh, well.... the
SPONSORS page here shows San Rafael Mitsubishi (I guess I might have to mention they're in San Rafael

), and Pro Street Industries over in Hayward just for starters. And the number of DSMs you see on the streets will show that many shops in the areas have worked on them, although I'd avoid the Mits shop in Brentwood like the plague, going by what they'd done to mine before I got it.
There was also one over on the Penninsula that got really good ratings, but I can't remember where it was.... San Mateo or San Bruno or dammit.
M&S Recyclers are all Mits and up here in Rancho Cambodia, and Road//Race Engineering is down in Santa Fe Springs.