Judith, you need to sign up for a lot of different companies and check the job boards regularly. Someone named Jacob posted a very extensive lists of MS companies on this forum. You can also get a list a www.volition.com - Click on the link that says Get Paid - then go to mystery shopping companies. Spend time registering with companies that conduct shops in your area. I have been doing this for about two years and am doing pretty well. I live in NY so there are a lot of businesses all over to mystery shop. I usually feel a little overloaded.
I hope this info helps you. If you want additional info or assistance, I would be happy to answer questions (in my own opinion, based on MY experiences).
If you want to have postings for shops sent directly to your email, Try joining Shadow Shopper. You could get a trial membership for a few dollars. They are an excellent source for mystery shop jobs-companies are looking to fill. It is like a "want-ads" for mystery shop companies.