When was the last time parts for a Barnack Leica were manufactured or available off the shelf? Who's suggesting you can't have these repaired anymore? So there you go, it's too simplistic to throw your hands in the air and wail, keeping cameras going is as much to do with desire than sulking about difficult to find parts. This isn't even true yet for a Barnack Leica but when the camera becomes rare enough to have a true value the parts will be repaired, sourced from damaged cameras, or remade. In the meantime it's going to be a fact of life that when a Nikon fails and it's too expensive to have it repaired, buy another.
As far as parts are concerned, you do not explore the never known before, the multiple ways of various 3D printing methods, polymers, metals, laser cutting from thin stock, small 3D parts scanners, the easily available metals, and other materials.
If I had to chose between having a decent shooting Leica, Minolta tlr, view camera, etc with a/several polymer parts or laser cut metals never used before, or having my inoperative camera sitting on a shelve, I'll take the mended camera, always.
I'll go further and suggest that photographers explore replacing parts that are prone to occasional failures, with more suitable and modern available materials that will function, at least as well and hopefully better than, what is being replaced.
For a personal example, I want to replace what I believe is a Bakelite battery cover on my Leica MR-4 meter, rather than simply mending with an adhesive, that may just snap at an inconvenient and critical moment.
Ask yourself, would you rather your prize camera, in my case a Hasselblad CM, working or waiting for an OEM replacement that may never show up?
Cheers