If you're willing to ship then don't limit yourself to just central Cal. If you want to go local head on over to your local Harley dealer and ask who they use. Also paint shops that specialize in hot rods or custom cars are a good source. I had Russ Foy of Custom Classics paint my last three Nortons and he does great work
Custom Classic Paint Works
30120 Se Rtreat Knsket Rd Ravensdale, Washington 98051
(425) 433-0712
Contact Blake Conway in Southern California. He is a great MC painter and has developed very close matches for many vintage motorcycles, including Nortons. My Norton Commando has won best in class awards a number of times with a paint job done by Blake. I've also seen a number of vintage Triumphs and Nortons painted by Blake and they are superb.
Blake Conway
2441 Green Hills Way
Vista, CA 92084
(760) 732-3950