does anyone serve green borsht ('shav' or 'schav' made with sorrel or spinach)?
can't find anyone who serves shav. saul's in berkeley says they don't but do serve red borsht once every week or two. the only borscht in oakland is red borscht from 4 HK-style cafes in Chinatown. a big bowl, either hot or cold depending on the weather, with a dollop of Greek yogurt on top of seasonal greens might be tempting.
Cinderella has a "spinach soup" that could be it. It's difficult to find a good red borscht in and of itself, and Cinderella's version is fine, but nothing terribly hearty, so I wouldn't get your hopes up.
Is Samovar Deli and Bakery still open? If so, has anyone been there lately? I know they moved to another location in Mountain View, IIRC
If that Georgian restaurant on Irving is still open, I think they served it.
Russian Family restaurant in San Bruno has it
No idea who might serve it, but I would also check Polish restaurants in the area, since sorrel soup is a very traditional Polish soup (can be found in local Polish grocery stores). By the way, that soup shouldn't contains any spinach at all, so if you happen to find one with spinach listed as one of ingredients, you are not getting a real thing.