if you can get a hold of raw milk, you can make your own buttermilk. this recipe is courtesy of Little Bits N' Pieces Farm:
To start your culture to make the buttermilk;
1) Allow a cup of filtered fresh raw milk to sit covered at room temperature until it has clabbered (usually 24-48 hours).
2) Place 1/4 cup of the clabbered (thickened) milk in a pint mason jar, add a cup of fresh milk (does not have to be raw at this point), cover, shake to mix, allow to sit at room temperature until clabbered.
3) Repeat this transfer of sub-culturing several more times until the milk dependably clabbers in 24 hours. Taste a small amount to confirm that it is tart, thickened, and has no off flavors. It should taste tart not bitter, for instance.
4) To then make a quart of buttermilk with this culture, add 6 ounces of the buttermilk to a quart jar, fill with fresh milk, cover, shake to mix, allow to sit at room temperature until clabbered.
5) Refrigerate.
Now, when you have a quart of buttermilk, add that to a gallon of fresh whole milk, let it sit until it thickens enough, usually 24 hours if the buttermilk is fresh, now you have 5 quarts of buttermilk. Generally, you add one part of your buttermilk to 4 parts milk.