Already occured (but will happen again next year)
Pin A Go Go http://www.pinagogo.com/ May 14-16 Dixon California
California Extreme http://www.caextreme.org/ July 17-18 2010 Santa Clara California
Pacific Pinball Expo http://www.pacificpinball.org/ Oct 1-3 2010
All of them are great shows and we're lucky here in northern California to have 3 great pinball conventions.
Also anyone else interested in pinball in the northern California area there is the Bay Area Pinball Association (BAPA) http://www.bayareapinball.org/
There are a number of players in our league who compete in our local tournaments, as well as the various California Tournaments, and even national and international tournaments. In fact the #2 player at PAPA A division was from our league (Andrei).
Pinballers are a dying breed. Play while you can...join a league...have fun.