Another potential source is a Corvette salvage yard in Pennsylvania called Contemporary Corvettes.

 

Ok, I am back from a little road trip. I spent most of the day with my buddy Jerry, and I did get to your axle questions. And I learned a little along the way. So from what I now understand the 44 was not used after 1979 because they changed how the rear end mounted in the frame. So an older big block 44 won't fit. (I was hoping) A for the third gen 36 accepting the 44 gears, he drew a blank too. I'm sorry I was not able to get solid answers, I guess we're both getting old.
I still think an off road 4x4 shop may be your best place for info as far as interchange goes.
Keep us posted, I would like to learn more.
If you want to see a few pictures of Jerry's backyard check out the C-3 section and check out my barn find thread.

 

I did see a Dana 44 with 3.73 gears rebuilt for 1600 on Corvette Central.

 

Strange engeenngineering.net has a 3.54 gear set for a Dana 36 $400.