Now that someone has named Meijer, responding would be an ICA violation regardless of what the OP edits.
It might help the OP more to suggest that she ask, in another thread, for companies who perform grocery mystery shops. She likely will get a lot more company names than she wants, but she is likely to get some. Asking for specifics and for locations is difficult. Although we help each other on the forum, we are all running our own businesses and we are competitors. Someone is performing those shops right now in specific areas, and they are unlikely to be willing to offer up their list of clients so someone else can grab the assignments. LeslieKay's post illustrates that, and I agree I would not provide specifics to someone because I am a competitor with others in my geographic area.
Signing up with more companies is the way I would go. Also, watching Job Boards might help. And there's no problem with asking "Who shops grocery stores?" and signing up with all the companies that are listed who shop grocery stores.