Exactly like Tara said - if you want to see more shops, you can set the search distance filter (in the upper-left corner of the Available Shops page, above the map) to 50 or 100 miles, and click the search button (a small magnifying glass symbol in that same row) - that will show you the available shops in the wider area around you.
Keep in mind that only a small fraction of mystery shopping companies use iSS. Outside of this platform, I'm with about 90 companies. There are another 100-200 that I will likely join in time. I've done about 75 shops so far this year - about five of which were through iSS. As stated above, if you want to make much, you will need to be willing to go more than a few miles from home.