The threads you're looking for are there, just keep digging. Interchangeability matrices, pretty pictures, the whole shebang. Another way is to visit the epc web site and xref part numbers there.
Parts yard axles are fine, provided their boots have'nt already failed. The boot on the replacement can be cracked just not leaking, doubt if you'll find any perfect axles in the boneyard. The OE's are pretty thick and rugged. A few months ago I swapped in a passenger side axle from a 83 240 in mediocre condition and everything's peachy.
A safe way to approach your issue is to wait until you find suitable donor parts. If the diff doesn't look the same as yours, you better make sure it will fit. That said, most 126 model year axles probably won't work and I vaguely remember something like that mentioned when I was researching. In the meantime, you can always implement the band-aid solution, read: shortterm. I packed greased up in both halves of the boot and a half roll of duct tape later, me and the girl were good for a month or so. Was far too busy back then. First result on the search list for that:
Factory CV Joints: Longevity w/o factory oil?
Now, use common sense, don't think this will last forever. Temporary, as in several hundred miles and even then no guarantees.
FNHB