Having grown up where I did, I've done more than my fair share of work, both direct and assisting, on John Deere, Ferguson and Ford tractors.
70 years old?
Yes.
Unavailable parts?
There's pretty much no such thing as an unavailable part for anything other than some of the rarest of the John Deeres, and if you talk to the right people, you can have unobtainable parts made.
I learned to drive manual transmission on a John Deere Model B.
Steinertractor.com has 30+ pages of parts for the B alone. And they're far from the only resource.
Finding parts of many Deere tractors, from the little patch tractors (not much bigger than lawn tractor but more capable) all the way up is about as hard as finding parts for the 1911.
Granted, finding one of the utility tractors with an integrated backhoe is a bit harder because most of them have been worked to death, then used for parts by people who are maintaining the ones that they have, but they're available.
So yeah, if I ever have need for something like that, I'll be looking for a 70-year-old version.