The only exhausts you can find are from a member, or ebay, no company makes these pipes anymore, unless you want a custom one made for a grand. There were several different pipes for the 125/175, a few that come to mind are PK, Bassani, and DG. The pipes are somewhat hard to find, but if you keep looking, you will eventually find one. I used to run a really nice bassani on my old 175 that I sold, and really liked that pipe. On my current 175, I found a PK for that. It is a lot better than stock, good increase in power all across the range, but not as good up in the high RPMs as the bassani.
The 175 front end will swap directly over, and Im pretty sure the 125 wheel will fit on the 175 forks, that would be my only concern, as the 175 had front brakes, but everything else will work. -- Jon.
THE 80's RAGE! Currently owns:
81, 85 Yamaha Tri Moto 125
83 Yamaha Tri Moto 200 x2
82,83 Yamaha Tri Moto 175 project
85 Yamaha Tri Z 250
84 Kawasaki Tecate 250
84 Honda ATC 70
85 Honda ATC 350X
84 Honda ATC 250R
(2) 84 Honda ATC 200x
82, 83 Honda ATC 185s
81 ATC 200
Lots of other parts and bikes