This is very discouraging since seemingly every vendor lets everyone buy their kits except Californians! Well fear not, because here's a list of distributors that will ship to California!
"Due to Regulations no California Residence Buyers. California Residence Please Check California Air Resource Board."
Helio Motorized Bicycles
Discount Bike Engines
Santa Cruz Green Motors
Venice Motor Bikes
Currently, the eBay user daoji888 is selling 66cc engine kits that come with a pull start and centrifugal clutch!
California-friendly eBay sellers:
Craigslist is also another place to look for engine kits at a discount price. They only come about occasionally though, so it can't hurt to check back every day because deals often come up! Click here to search for motorized bike stuff on Craigslist!