Just to add, there's more info here:
http://www.356car.org/
Quite a large group, with five chapters in northern California, each with its own monthly breakfast meet. I think they started up a number of years ago wanting a group just for 356's and something a little more laid back than the PCA.
On paper, they're open to anyone 'with an interest in the 356', meaning you don't have to own one to join. But if you show up with a replica, be prepared to defend yourself.
One guy told me he was running his C coupe with a VW engine while his real motor was being rebuilt. I felt his pain.