We buy shelf and fridge stable buttermilk powder. I like chicken soaked in buttermilk either before dredging to fry or as a flavor enhancer for grilling some chicken pieces. The biscuits I like best call for buttermilk.
As far as I am aware our local supermarkets do not stock buttermilk. "Tops" supermarket do stock some Waitrose produce (very expensive) but not buttermilk. We also have Tesco but it's branded "Tesco-Lotus" which is a Chinese run consortium. No buttermilk there either. It's not really surprising given the lactose intolerance of the majority of Asians. I suppose that I could make it myself but I've never really had the need.
Replicating a dairy free buttermilk is high on my list of 'wants.