The tapered roller bearing cups in the wheels are replaceable. They're just pressed in, and can be removed without much trouble.
I'm assuming by "axle shafts" you are referring to the spindles in the carriers that the idler wheels rotate around.
They aren't too terribly expensive from Tucker, and almost assuredly they have them in stock. One nice thing about buying parts from Tucker is they ship promptly, and they don't treat the shipping department as a profit center (at least they didn't the last time I bought parts).
I hate to be the bearer of bad news, but if the spindles haven't been removed since your machine left the factory, you may be in for some serious work. They have a tendency to "rust", "corrode", or otherwise become "frozen" in the carriers, and can be a real PITA to remove.
Last year on the advice of Tucker's Jeff Godard, my snowcat buddy and I decided to remove all the spindles from the carriers and coat them with Never-Seez prior to re assembly. Even with the carriers off the machine, and using a hydraulic press, we had some that refused to cooperate. It took multiple cycles of heating with an acetylene torch, and a lot of force to persuade some of the spindles their best option was to come out.
Doing it in the field, laying on your side on a tarp and trying to swing a BFH simply would not have worked. I sincerely hope yours come out without a fight.
- I need at least one wheel for starters and probably several axle shafts 