Has anyone seen any 6" hamster balls for sale? I've searched everywhere but I can't find any.

Most of my dwarves prefer the 5" ones but they're a little too small for a couple of my bigger boys - but they find 7" balls a struggle to move around. Its a bit like Goldilocks and the three bears (or balls in this case)...too small, too big....I'm looking for a ball that's "just right". Any ideas anyone please?