If you need a 260z clock, I may have a spare or 2, but assume they are also all dead! But like anything related to these cars there is several different variations of clocks fitted to these cars depending on your year/month of manufacture.
I believe Ron can repair nearly all the Z clocks, but a couple of years ago he was struggling to find parts and I believe the situation has only got worse as these cars become more valuable, less are parted out, parts thin out. So you would need to send a clock across for repair. For a 260z simply replacing the capacitors and resistors would probably be all that's needed to go them going again. For the early 240z (Jeco) clocks, replacing the inner guts is probably the most sensible option because even if you can fix the old mechanism they seem to fail again relatively quickly. I suspect my test bench had a more consistent 12v than in the car and that was enough to drive the clock, as soon as I put it in the car. Nothing.. lol
Hence the 280zx clocks had a Quartz movement that was fairly reliable and easy enough to swap into the 240z/Jeco housing. But I used to be able to find these cheap and now I can't find them anywhere!
Ron was having a hard time finding a suitable alternative too, but maybe he's onto a better solution now?
https://zclocks.com/
Honestly I can't recommend Ron enough, he's restored several rally clocks for me and always did an excellent job.