<<Disclaimer: Verify this information before applying it to your situation.>>
If you can't or don't want to use buttermilk in a recipe, there is a
viable substitute---plain yogurt. You can easily find it in various
forms--besides cow's milk, you can find goats'milk yogurt and non-dairy
yogurt.
Some of the yogurts are very thick. Just thin with water to the proper
consistancy. I have found that a six ounce contain mixed with 2 ounces
of water yields a good consistency. I have used this in muffin and
cornbread recipes. Never had a problem~
Ann