Until you sign up with a mystery shopping company and sign their Independent Contractor Agreement (ICA), which usually includes a confidentiality agreement, most companies will not disclose the names or locations of their clients to you.
If you want to get an idea of recent jobs in your area, you might try JobSlinger. The jobs posted on JobSlinger are probably old, and I doubt you would get any assignments, but it would give you an idea of companies that had recent jobs in your area and you could sign up with those.
I found it more time-effective, when I was starting out, to go down the list and sign up with all the companies on the list. After signing up, I could look at their job boards and see who had which jobs in what areas. Some had jobs in my area and some did not. But, just because a company does not have a job in your area right now does not mean they will not have clients in your area next week, next month, or next year. Some of my best assignments have been with companies who had no jobs in my area when I signed up - but they suddenly got a big client - and I was signed up and ready.
It does seem like wasted time to apply and to then learn the company has no assignments posted in your area, but, on the other hand, the time spent is time invested in your small business. Most small businesses spend time advertising their services and following leads that ultimately do not result in a job.