David,
if you find a 125a/b/c rear hub {as they're all the same} and have trouble finding an offset/dished sprocket for it, an AG100 steel sprocket will bolt straight up, just need to drill 2 extra holes/simple,available in 47t or 51t.
front hubs as Nathan said are real common to most early small bore Yammies, its just the brake hub with no speedo fixture thats the tricky bit to find. or, just grab a conical hub from a 250/360 as they're still pre75 legal and more common.