I needed a very similar bolt for my 185S recently. I found it at a local hardware store. I think the thread count is something like 1.25.
Put your butt on the inside fender or end up on the ground!
TRX450ER
ATC250SX
ATC350X
ATC110
ATC185S (Marlboro Red)
XR100R
CRF230F
Raptor 125
Breeze 125
Grizzly700