Might be able to identify who made them with photos - unless you can do that, finding parts are hopeless.
Once you do that, might contact Dick Janak through ORCA.

As fishing reels go, spinning reels are amazingly complicated mechanisms. I always say the 1932 Hardy patent for the Altex was the Space Shuttle of fishing reels.
They're even much more complicated today.

Even baitcasters, with their modern improvements, are still a basic mechanism.

and that's a great idea - cannibalize a few for parts and assemble the best of the bunch.

looked on ebay, look quite similar to the South Bend Classic 925 Japan-made reels.
Here's a tutorial on the 925 - https://alantani.com/index.php?topic=28146.0
Another similar reel is the Shakespeare 2200 Japan-made - not the Sigma series, but the predecessors, usually labelled 2200 Ball Bearing. This was made by Omori in Japan and it looks like the Diamond is an Omori brand too.

The only parts available for the Fury or the SB or the Shakespeare will be on ebay maybe.
Bad news is the SB Classic 925 has started to attract collector interest, and these are both rare and selling for relatively high prices.
In general the ultralight spinners are more in demand, so harder to find and pricey when you do.

I have a SB 930 and it's a terrific reel, well designed and solidly made with a good drag. Just have to get over that made-in-Japan thing.. this is much better than I remember the Daiwas etc from that era.

Best bet as folks say, is to look for one on ebay as a spares reel. The roller guide and the bail spring are what usually break unfortunately.. I was able to find a roller for a Shakespeare 2052, and a bail spring for an Orvis 50, so it is possible though may take some time.

Here's the schematic and parts list for the SB Classic, courtesy of the good folks at alantani: