jay, if the part is suitable for CNC manufacture it can be useful to go through the exercise of setting up the job on CNC. Once you have a debugged CNC program to make a part, you can go back to the engineering company any time and get one part made, or half a dozen. That creates an easy opportunity for you to become the new supplier of odd bits like the wearing parts of an SB mower. You don't need to make them yourself, you just need a drawing of the blank plus a CNC program to finish-machine it. I suspect that is the long term solution to most problems concerning parts for vintage cars, motorcycles, mowers etc.
