Its a 3500lb axle, not much special about that.
You do need to know the full length from outside dimension axle stub to stub, if it straight, drop, over spring or under spring mount.
Drop axle, you will need to measure the drop..
Any reason as to why it needs replaced?
If you think it is bent since it has a "bow" in the middle of the axle, it is not, that bow is present intentionally (darn spell check changed it to something else) and is normal when unloaded, when loaded that bow will straighten out some. Without the bow your tires will scrub off the insides when loaded.
If stubs are damaged from seized bearing, they sometimes can be cleaned up and used again, carefully cut off seized bearing races and then smooth and polish stub but sometimes result is catastrophic like damaged threads, deep galling..
Bent stub?
Yeah, then axle replacement most likely needed and perhaps a few other parts..