I can't answer your question about LA area dealers but you should be able to look them up in the phone book or on-line. I'm sure that a lot of the bigger dealers will have web sites that you can explore.
Another opportunity will be to visit any of the local coin shows that are in the LA area. Most of the local dealers will be there to buy, sell, and trade coins and probably currency as well. Collect their business cards, check out their wares, and talk with them. It's a great way to spend an afternoon.