I was introduced to "LAX-C" recently by a friend downtown. It's a Thai SUPERMarket that has everything you need to prepare any Asian dish. My friend lovingly calls it the Thai Costco and he's not kidding--the place is HUGE. There's also a mini food court that sells Thai food (unfortunately, I did't get a chance to sample their offerings). They apparently do a lot of wholesale biz w/local restaurants, so many of their products are sold in bulk, but its not mandatory to buy them in bulk.
The location is a bit scary...its in an industrial area between Chinatown and the Brewery arts colony. There's a small parking lot in front and its free! The address is
1100 Main St, Los Angeles.