Briggs flywheel keys are usually made out of zinc so they can be sheared when the blade impacts something with enough force so that if the key did not shear, the crankshaft would break. If you have to make your own Woodruff key replacement, zinc will be hard to come by and you may have to make it out of aluminium. Do not use a steel key, such as the blade boss key, or the next time you hit something your crankshaft will fail in torsion. I think you have little chance of buying parts for that engine, but to find out for sure you should send a PM to Bruce, the Outdoorking site-owner: he will know for sure.

Here is the last Woodruff key I had to make - must be nearly a year ago now:
[Linked Image]

It is fairly straightforward filing.