Parts for popular old tractors such as the 135 can be picked up from any dealer that has an account with an aftermarket parts company. I listed the gasket for the shift plate on the top of the tranny, re reading your post I realized I looked up the wrong gasket. I believe the proper number for the pto lever cover on the left side of the transmission is 181217M1. You will most likely pay a premium if you buy OEM, you could also buy some roll gasket material and make your own.