Dry powdered buttermilk can be found in the baking aisle at most grocery stores. I like to use it in this mix because I rarely have fresh buttermilk on hand when I have a craving for pancakes. Once opened the dry buttermilk does need to be refrigerated however, causing this mix to need to be stored in the fridge until ready to use.
I understand that not everyone has enough room in their fridge to store 3 batches worth of pancake mix, so you can omit the powdered buttermilk in this mix if you'd like to store it in the pantry. When you're ready to make pancakes just omit the water called for and add 2 C of fresh buttermilk instead.