TT250/350/600 have 43mm forks, which will go onto the IT using the TT (or later It, or YZ) triple clamps.
The DT200Rs have 41 or 43mm forks (depending on what you read). The fairly rare DT200L (with the single sided radiator) might have 38s, but I doubt that the forks would be much good.
XT250 should work? But soft springs, soft valving and not much travel.
I've seen a whole TS250X front end grafted into an earlier IT, but again, they're a trail-bike fork so they're probably a step backward on an enduro bike.
Personally, I'd got for the mid~late 1980s YZ/TT/IT200 front end.