That's a tricky one, tracks often are a problem with vintage sleds. Once you get new enough, the 15" wide, 2.52" pitch became almost universal; that's not until the 80's though. I found a track dimension of 111x15" for the '74 Sno-Twister, but maybe the model you've got is shorter like KCCats said. The shortest track I see widely available is 114," which wouldn't be terribly difficult to adapt to if the pitch and rail width is right. 9" (center to center) is the standard rail width, and if it's a 2.52" pitch that would make things easy. 1.97" pitch tracks are still available too, in case it uses that. If you're looking to do much riding with it, then running a new track would be a good idea even if you have to do some adapting – better traction with newer designs and no worries about it coming apart.
If the new route is a dead end, then it's down to scouring the internet and swap meets for a used one. That could be a lot of work: they're out there, but the price may be steep and even a "new" (unused) original track might not hold up so well. You're in a good area for swap meets, so that might be worth your time (plus you can get a hands-on assessment of what you're getting).
Anyway, I just looked up the Sno-Twister, and found this article: https://www.snowtechmagazine.com/snotwister/
. Sounds like a pretty cool sled, and being a dominant racer really ups the appeal. I hear what you say about that sled in deep snow. Nowadays a 144" is the shortest track you'll find under a "mountain" sled, and most guys go with a 155 or 163. You can get by with a 136 on more level ground in deep(ish) stuff, but I can't imagine trying to get around on a 111x.5! Then again, I do more off-trail riding than on. I'd like to find a cool vintage sled to tinker on and tool around the trails, but I'll stick with my RMK for the deep stuff!