Mama Lan's in Berkeley (on Gilman) is getting their first shipment of soft-shell crab this morning (Friday).
I was in the restaurant and overheard the proprietess say as much myself.
So if you want it fresh...
I think a crab prepared with garlic costs about $28, so it ain't cheap, especially considering the humble setting.
If you don't want crab, it's a great little place and there are other dishes worth trying: a chicken roti and a catfish soup among them.