You can sour milk by adding 1T. lemon juice or vinegar to 1 C. of milk, but to me, it's not the same as real buttermilk. There is also a powdered buttermilk that you can use and store in the frige, you can order it online if you can't find it in the baking section of your store. Again, to me, it's not the same as buttermilk, but many people use it.
As for sour cream, you can use plain yogurt sometimes, but if dairy is hard to come by, maybe the yogurt would be too?