Grocery store websites tend to show very, very little of inventory. The typical grocery store considers the data a trade secret, and are unlikely to tell you if

Grocery store websites tend to show very, very little of inventory. The typical grocery store considers the data a trade secret, and are unlikely to tell you if you ask. You could walk around the store with a camera mounted to your hat (seriously) and then work from the images. You are more likely to get data from smaller stores than from big chains, but they tend to have less accurate data (weekly inventory rather than real-time). But I don't know if you will get far without the big stores. If they notice you gathering data they may get suspicious. One trick would be to ask people to upload receipts from stores. Then you work from the product listing on the receipt. This will tell you where people are buying things also, in the sense of "Store X is where most people in this area buy product Y." Think about it, this might be the easiest way.