The axle shaft will not necessarily all be the same in one axle model. So forget about figuring out the exact model. Start by looking on the flange of the broken axle for shaft numbers.
Rockwell axles often have ( ) around the center of the flange, while most other mfg are flat faced.
You'll need to know spline count, length and flange diameter and bolt count/circle.
Many axles had a course spline in early years and have gone with a fine spline in the same axle model.
For example, you can have a IHC 472 with 20 spline or 39 spline, you need to know what you are looking for.
If Rockwell axle you can find some of the half shafts in the attached manual.
Foote axle is another source once you know what you need.