I start a product location search site. the idea is retailers give us the data of their products, so that their users can search their products by location and keywords.
We've got a problem, how to get the retailers to give products data in our site? it is like a chicken and egg problem, they would say our site have not enough products, so that they don't want to bother with giving us data.
The answer to this conundrum is money, lots of money. You'll need a massive cash injection to build out this idea and convince enough retailers and customers that it is a viable marketplace.
It is possible, but VCs seem to be getting nervous about B2C malarkey like this after a number of investments that have been less than optimum.
Another approach might be to "fight from the inside". That is get hired by one of the big retailers to set up such a system. Or get hired by Google and do this in your 20% freetime (if they still do that).