It is in the cleaning aisle with Bartender's Friend, Comet, soap pads. I use it to clean copper - it works well and is inexpensive compared to other products. I agree, the supermarkets usually have it. They have it.
Many hardware stores stock it too.
I recently visited my parents in W. KY, where they had just started carrying that product in the local Super Walmart. It had been a while since we had seen it any where as well. I'll try Scnucks. I've checked super WalMarts here and in the Quad Cities to no avail. Before posting a message, please be sure you are in the appropriate category.