This party is not in SF, but I'm sure you could click around and discover some west coast folks who attend: http://atparty-demoscene.net/

Also, see Pouet.net for all things demoscene.

Your're in luck there's still an Amiga group in the general area (San Jose) http://www.calweb.com/~rabel1/ If no one replies here directly, this would be a good avenue to check out.

Otherwise this is the best I could find for US demoparties http://magfest.org/demoparty

Check out https://www.facebook.com/groups/NAScene/ and see if anybody there is local. If not it might be great to start one up! Remember, us old sceners managed to build a decent East Coast community pre-Internet, it should be easy these days!