In place of buttermilk, you can use:
1-1/4 cups / 310 ml milk stirred with 1 tablespoon / 15 ml lemon juice or vinegar. Let sit for 5 minutes before using in recipe.
3/4 cup / 185 ml sour cream mixed with 1/2 cup / 125 ml milk.
1 cup / 250 ml plain yogurt mixed with 1/4 cup / 60 ml milk.