Difference between 23-222C and 23-222B

Good question. The manufacturer of these rollers, Stanley, likes to upgrade them every few years. There were several iteration of these rollers before the 23-222B. To be honest, it's not entirely clear why they keep updating these rollers, but we do our best to keep up, and in our opinion the 23-222C is the best and most versatile of the lot, so it's what we usually recommend even though we keep stock of the 23-222B as a backup option. 

I'm afraid that the wheels themselves are not sold separately. These are only available as a complete unit.

As for why we recommend the 23-222C over the 23-222B, it's simply because it performs better. It's a newer model that the manufacturer made explicitly to replace the 23-222B. The 23-222B is still a viable option, however, even if it doesn't work quite as well as the 23-222C. It's up to you which one you'd rather go with.

As long as your existing rollers are in good condition, you should be fine reusing them. However if the one side failed then odds are that the other side isn't far behind; it's probably a good idea to replace the top and bottom at the same time, just in case.