The only BBQ centric event that comes to mind is the annual competition at the Gene Autry Museum in April, see http://www.autrynationalcenter.org/bbq.php
Many BBQ restaurants and caterers show up at festivals, search local newspaper sites and check out this list: http://email@example.com
A little more searching of this board may turn up something else, good luck!
What you're looking for is a rib burn off, which is different than a contest like the BBQ'n at the Autry event. Rib burn offs are events where vendors sell directly to the public.
Contests are judged events where the competing teams are not allowed to give food to the public. Event organizers may bring in non-competing vendors who cook for the crowds, as they did at the Autry contest. Fine event. Looking forward to competing again at next year's edition.
Check out the event schedule on the California BBQ Association, which will announce BBQ events across the state