Just look at the differential vent. The old style had a metal cap with a wire retainer sticking out of it, while the later style had a plastic vent cap
That's what I was going to suggest, to find a decent used older style differential. I know there are LOTS of them lurking out there, and if all you need are the bearings, then it would be less bulky to ship just those. Although you might also need the axles as well, since the bearings rode directly on the axles in these early differentials, and if the bearings are damaged, the axles probably are as well.