Look at the Official List of Mystery Shopping Companie which appears at the bottom of the page. Be warned that the list has not been updated in several years and some of the companies no longer exist. Don't be discouraged, simply keep applying to companies. Market Force has shops all around the country. There is no way to know which MSCs have shops in your area until you apply and look at their job boards.
Shopping Southeast Pennsylvania, Delaware above the canal, and South Jersey since 2008