In Southern CA (San Diego county) you can find whole briskets at Sam's. That's where I get most of my smoking meats. I recall seeing them in Smart and Final as well but the prices were slightly higher.
Once upon a time I took a trip north to a SuperWalmart. We do not have one in SD county at this time. I did not buy a brisket that trip but the butcher claimed they had whole ones. Perhaps this could be verified by others.
I too would be interested in other sources.