Hmmm. I don't know that "all" is possible. I have two yahoo stores and they are pretty much 100% customizable, so there might be almost no fingerprints left that indicate it is a Yahoo store.
At some point, however, it will have to have a link to the shopping cart. That will have a link that starts with order, store, yahoo, net. (Sorry, I'm still a newbie and can't post URLs. Take out the ", " and insert dots.)
I'm not the Google search term guru, but I would think that there's a way to get Google to return a list of URLs that link to that URL.
Good luck!
