Try the Openair Market website at http://openair.org
The have an older but still mostly accurate list of California farmers
markets from the California Federation of Certified Farmers Markets. They
also have lists from other states. This
is a great place to start and a good site.
For a list of every Extension agent in California, try the Small Farm Center
site form UC Davis at http://sfc.ucdavis.edu/
My experience is that not every California extension agent is availble
electronically but their snail mail addresses are there.
Hope this helps
Full Circle Organic Farm