Back to your question about the Cream of Tartar.... it's used to stabilise and add volume to beaten egg whites. I assume (because I've not made the oopsie rolls yet) that they are made from beaten egg whites???
As said previously, it's found in the baking section near the baking powder, bicarbonate of soda, flours, etc.
Again, I am wondering why I am the size I am...maybe something to do with being so familiar with the baking aisle!!! LoL