Coleman doesn't have one, I checked with them before posting. Everyone that shows they have them online actually doesn't.Coleman equipment, $112.33. Put it on order and it can be shipped to you direct.
Yeah, it's the large roller in the back. It's 6 inches wide if I remember correctly....Probably a specialty item. I believe the bearing opening for the "axle" is 3/4" as well.Have you just tried searching for generic wheels? Lots of them are similar, you might have to put a bushing in em, or buy a pair to even things out, but, hey whatever gets you there...
http://www.surpluscenter.com/Wheels/