Wow, that's a hell of a job!
The Frontier also uses M226 rear axles (if you're in the market for the whole shebang, now would be an excellent time to do an spring-over-axle swap/lift!) so you could potentially source a shaft from one of those. Titans have M226s as well but their shafts might be different. I don't know who if anybody in MA makes axle shafts but if it came down to it, you could bring the original in and have a new one made.
Now, I've never swapped a shaft before, but this video seems to make it relatively straightforward:
http://www.youtube.com/watch?v=gzh8ivv1EF8Also see here:
http://www.jeepforum.com/forum/f140/how ... ly-377533/Disassemble, don't lose anything, replace what needs to be replaced, remember what order everything goes back in, torque to spec, at least that's how it seems to me. But don't take my word for it.