Amayama said there was 1 left and 1 right rear backing plate available with a 64% accuracy of availability. I went ahead and pulled the trigger on ordering them - we'll see what happens.....will update if this actually works just for anyone else who finds something on amayama -

MS parts came back and said they don't have anything for gen 1's right now that can't already be found new on CARID or similar sites.

I submitted a couple of requests to that other national junkyard database - if this doesn't work i'll probably have to try to get refunds for the rear brake parts that I got and just try to find someone who will do the rear disc conversion and find a down home cousin shop to certify the inspection. Might have some rear brake parts to sell if I can't get refunds - I bought new drums, hardware, shoes, cylinders & self adjusters.
Hub parts are hard to find but the existing ones on mine look okay at first glance and they've been working fine without any issues driving the vehicle - just need bearings.

**EDIT** - UPDATE - so it's looking promising. I just got a notification that the order was accepted and they initially provided a delivery date of March 25th, then they updated the expected delivery date to April 05 - I checked the listing for the part again and it had been updated to "out of production" - then a few hours later they updated it again to show availability of "1" again for each piece - not sure what that was about - the "glass half full" in me wants to think they talked to the supplier and verified they still had a few available after my order - but the "glass half empty" in me thinks maybe it's just some automated process on their listings. Hopefully I get a notification that something actually shipped in the coming week or two - i'll keep this post updated with progress.