You can use just about any ATV or MC master cylinder. Ideally, it would have a 1/2" bore (marked on the casting) which is pretty standard for Honda ATVs.
I have a CRF front master on one of my 84s. It's 12mm diameter and the brakes are a little mushy.
If you're buying the parts (vs having them just laying around) get the newest you can afford.
Brake lines are pretty much universal (10mm banjo fittings) and lenght is the only critical consideration.
I don't know if the 1st gen 200x is the same length as the 2nd gen but I seriously doubt it.
Do you have a caliper? Is the 2nd gen X caliper same as the 350x/250R?
i have the caliper, but not sure if its locked up or not. i have no rear brake parts other than the disk. with the front, i just have the disk and caliper. if the caliper still works, i just need the master cyl/lever setup, and a hose
1986 Honda ATC200X
2005 Yamaha Road Star 1700
ToyHauler- 1998 Ram 3500 5.9L Turbo Diesel