Yeah, I don't know about San Francisco specifically now that Grant's is gone. The Piedmont Tobacconist is an easy BART ride to Oakland and they have a very nice shop with some excellent bulk selections, including Samuel Gawith. It's in a cool neighborhood that's worth a visitor's time anyway.
The only tobacconist with a good selection in the Bay area is Telford's in Mill Valley.
There isn't much else. The Piedmont is a nice old store, and was the birthplace of the Esoterica line, but the selection isn't terribly diverse.