- try one of the raw milk vendors at the farmers' markets
- buy Organic Pastures raw milk at Erewhon, Santa Monica Co-op or Rainbow Acres and make your own buttermilk from it. (Whole Foods used to carry Organic Pastures but i think they're having issues with the company because it's "temporarily unavailable" at all their stores.)
I know you are looking for real churrned buttermilk, I have been looking for it for years here, it seems to have disappeared around 1960. I know they have it back east and south, but I cant find it here either. I think organic pastures used to make it but I dont think they do anymore. I made it myself by getting pure cream and churnning it in the kitchenaid, you wind up with butter and the liquid buttermilk, but it is sweet, on the farm the natural bacteria in the air would ferment it, what i do is add a little cultured buttermilk and let it stand for a day then refridgerate it, it is pretty good, baring that smart and final carries alta dena buttermilk, cultured, it has a good tang to it, Good luck!