The Jolly Oyster. The only oyster farmers in the area. They have two locations around Los Angeles.
Ventura - They have a shuck shack located right on the beach where you can shuck your own oysters or have them shuck them for you. You can also buy items like scallop ceviche, oyster tacos, baked clams etc.
If you are adventurous, you can grill your own oysters, clams on the grills provided by the state park right on site.
Torrance - They opened a very small market where you can purchase clams, oysters and pacific crab claws to go. The oysters are farmed at their two farms in Baja. Oysters are only $1.25 each or if you buy 40, they are only a $1.