cant find 8 3/4

The chances are VERY SLIM that an A-body 8 3/4 is going to be sitting in a junkyard at this point. Your best bet is going to be on forums such as this (as the mopar guys have already gotten them from JY years ago) or local shout out options such as Craigslist. I have had best luck with a forum post, asking for what is needed, and CL to gather offers from people who have the axle, and are willing to part with it.

FYI