Inte,
The best place to look is at Biodiesel.org--they have a listing of retail Biodiesel sites.
When I purchase it--I get it from ITL fuels in Cudahy. Price ranges usually around .18cents above diesel for B20. Last night D2 was $2.36 so I would imagine B20 was around 2.53 to 2.54.
In San Diego I know of one retail outlet called RTC fuels in El Cajon blvd. I am cautious about them because they use recycled oil--whereas ITL uses virgin Soy.
There is another retail site available in Ventura--they several B20 pumps and one B100 pump. They use Virgin soy. It is called T.W.Brown Oil company.
Be cautious of where you buy--I had the fuel from ITL sampled and analyzed by AVlube and it came back excellent.
I hope this helps you.
Ron