A number of places...
Don't buy it from European Motors in SF or Oakland as they always overcharge and will try to rip you off if you don't know exactly what you should pay. I have tried unsuccessfully to buy a number of cars from them and always run into a 'dealer' mentality (pretty much the same attitude as Weatherford BMW-yuck). Hopefully the slowdown in the economy has changed their willingness to negotiate but I doubt it. The dealer in San Rafael had a couple of 430s last time I checked and they seemed pretty nice. Also, I recently put a deposit down for a new SL with James Sullivan at House of Imports in LA 714-562-1194 and he seemed really easy to deal with and willing to work with someone to get their business. Good luck as there are a number of 430s out there so you should be able to find a good deal.