FDD, I found my doctor listed in canorml.org, just picked him out of the list (he was closest) and walked in with my medical records.
He's legit, just down the street from my house, and charges half of what medicann does. As part of our contract he'll subpoena the courts if I'm ever arrested for pot, and he'll sue any state officer if they report me to the feds. What service.
Here's a link to a list CA MJ doctors:
http://www.canorml.org/prop/215physicians.html
PS: I've been burned by fake doctors before too. Make sure you're talking to a "doctor" and not a "physicians assistant."