Ratman, You can always go to hotbot or google and search for rat toys, but I've bought from 'The Ferret Store.com' and petsmart. But if you don't want to but any thing you can always hang a papertowel roll from shoestring and tie it to the top of the cage, depending on the size of the cage of course. My girls love the boxy shaped Kleenex boxes, they get in there and haule bedding and nest or they chew on the inside, they also hide their treats in there, but make sure you rip out the plastic that's is just on the inside of the box.
Have you tried a ferret ball, or I guess it's for cats too, but it has a bell in it. My girls love that too.
Personally I think you can make toys that your rats are going to enjoy possibly more than store bought toys. I you have any rope or a feed store that sells rope, just hang it from the top. They LOVE to climb.How big is your cage? I decided to build the girls a bigger cage about 2 months ago, and it doesn't have any shelves or anything but they like that because nowthey can climb all over the place. Their cage measures 3 foot 3 inches long, 2 foot tall and 17.5 inches deep. I made it myself using the suggestion that I got off of a rat site called 'Rats in the Workshop' www.geocities.com/ratsonthehill/cagecrafts.html
So maybe you can get creative like I did and build a big new cage. I only spent $22.00 on their cage and I used the ideas from 'Cinder the rats cages'
Hope I helped a little