If I may be bold and "correct" your thought process by saying: " You want to find mystery shopping OPPORTUNITIES in your neighborhood" opportunities vs. companies.
Many companies have opportunities all over, some are even international.
So, to do that all you need to do is:
A) Visit the MSPA and the IMSA web sites.
B) Sign up will the companies on these lists. As many as you want.
C) The schedulers will contact you when something close to you comes their way.
You can also launch your own search via these MSP's web sites/Apps and see what is around you, and ask for the assignment(s).
This is the reason MSPs exist. The clients go to them, and we, ICs, go to them and the circuit is closed.
Hope this helps...