Just got a vaccine appointment for tomorrow! My niece on the east coast was looking for San Diego County appointments for her dad, and called him when she found some available. He called my wife and I got online right away. Lots of forms to fill in, chosen time was full so I had to go back and pick another, but I did get the confirmation.
They only open up appointment slots when they have vaccine in hand, and the slots fill up in a few minutes. So that was a stroke of luck. And the cool thing is it's the only drive-up vaccination site in San Diego County.