Oh man, good to see an old Deuce. Those were a cut above the rest of the regular "karts" but it really is an early UTV/ATV.. I don't recall seeing too many of those around, like here on the forum, so maybe it is a big deal. A fairly rare bird to me anyway.
Good luck on the parts, man

. I'd say look for something you can adapt to fit but that is a fairly complex vehicle. If you really wanted to give your grands a taste of your youth I'd recommend a more regular, conventional kart that is easier to fix. Something like a Yerf-Dog, Murray Explorer, Manco Dingo or any similar variations on the theme with full suspension. One kart for each!
For reference, what are you looking for, is it:
10326-16 AXLE WELD 24.789 LG DANA
10327-16 AXLE WELD 23.539 LG DANA
...or something else? We got guys with good Gewgle-Fu skills