When you go to the link for the 'Official Mystery Shopping Companies' at the bottom of each forum page and open it, you will see several lists of companies (Most Discussed and then a fairly full list). Click on, for example, Market Force. When it opens you will see a link to the company's website just below the company name close to the top of the page. That is to take you to register. If you don't immediately see a 'Register to become a shopper' type note on the page, go to the shopper log in page and you are likely to find a link to register.