I'm not sure where to find those parts as sometimes with older motors if you ask a mower shop they will tell you that new parts are no longer available.
Then if you can't buy new replacement parts you need to look for someone in your area that makes custom parts.
The problem sometimes is getting the parts made costs more than a new replacement motor.
If I'm after a certain type of motor that has to be original, I would search swap meets but it can take a few years to find the right motor at a good price.
I had a good running G40 motor that I sold about 3 years ago for $30. so it may just be cheaper to find a good second hand motor.
I think I still have a good G40 on a generator I was given years ago so they must still be around just takes time to find.