Welcome to BF !
I don't think you'll have too much trouble finding parts for your bike...people here have been known to just send parts off to people who need them or will know what direction you should be looking.
As far as oldest functioning bike tyres...I was running a Dunlop Dragon on my old Raleigh that had no psi rating but just a script that said "fill until hard".
Now it hangs on my wall of fame since a few hard brakings peeled off some good swaths of ossified rubber.
Running the same tire and tube for 17 years is impressive... it's probably not all that safe... but impressive.