So where do you find those companies that pay for your services so that you can become mystery shopper

For mystery-shopping information go to Mystery-Consumer.Com or MysteryBuyers.Com which is a great starting point. This is the place to go for feedback on a company and to look for the free list of companies to sign up with.
TIP: You will be an Independent Contractor and companies are required to send you a 1099 for your tax return, once you reach $600 income with them. Keep good records.

As an experienced MSPA certified Gold shopper I network with other shoppers and have established a good reputation with several companies. I find networking essential to be a successful shopper and believe the mystery shopping forums play an important part in keeping shoppers motivated, on track and informed. The good news is you are an Independent Contractor and you can pick and choose your assignments and have fun along the way, have a nice part-time income or decide to walk away at any time.