If it needs it, why not any of the Krag or 30-30 based cartridges. The 6mm, 25, 6.5, 7mm alternatives are all available as are larger bores. Cases are readily available and a couple of hundred should last quite a while.
That 22" barrel will influence choice some, but while shorter than normal for a single shot, it really shouldn't affect performance.
Figure what you want it to be in it's next life and go for it. However, I would shoot it with different weight bullets if you're able to load up some ammo. It may well surprise you.
