As has been stated, the IBM Selectric typewriter standard font is a good approximation - IBM made most of the printers and computers in this era so that makes sense. My Fremont 1972 Lemans needed one 25+ years ago and that was what I used. When I used to repair them for the junk man back in the '90s you could get them cheap and I also found that the typeface head was quickly and easily replaceable with different fonts that were available from IBM. I would hazard a guess if you trolled sales or found a weirdo who likes old typewriters they could easily locate the type heads with the various fonts.
Finding something modern that approximates it is something that nerds have done for other fonts - namely
Gorton (link) among others.
Edit to add:
This guy right here (click) has a wide variety of font balls and examples of each. I bet if it was ever made by IBM you'd find it there...