Stanford plays at Cal on Thursday evening, February 16th. According to the Cal website, single-game tickets should be available now. However, we tramped through every available path and were not able to buy online.
Then we tried the "live chat" option found at the bottom of this page. The person on the other end of the chat was Patrick, at the Cal Ticket office, who was very helpful.
Try the chat first. If that fails, you might try calling Patrick at 510-642-2699. Be sure to tell him you hear he is super nice.