Are you going for a proper 100% original resto, or a ride bike?
The basic motor was only used in 1979 model YZ250/400, and 79/80 IT250/425, FWIW.
Front spoke kits are almost universal among Yammies of the era - everything that had the 322 or 1K7 front hub uses the same spoke kits.
Front brake plates are much the same. Any single leading shoe YZ/IT brake will work, providing its from a bike with a conical hub and leading axle forks.
For the 'bars, passable copies are available if you look around. Originals are rare, but you shouldn't have to pay much if you find them. For a ride bike, just get some 764 Renthals and be happy.