We stopped by Johnson's on the way to the beach yesterday, and found a new (to us) name and ownership: Drake's Bay Oyster Farm.
I bought 2 dozen large (a dozen for $10) for bbq'ing; the name may have changed, but the oysters are still delicious. Chewy, but not tough, and very sweet. We grilled them with Meyer lemon and garlic infused butter, and the adults had to fight off the chowpups for the last of them.
Please note: Fire permits (no charge) are available at the Pt. Reyes National Seashore Visitor's Center and necessary if you want a beach fire.