Unfortunately, that part is pretty much a "unicorn" as far as availability...
A couple of choices immediately come to mind:
1. Purchase a used beater donor HS-40 engine or short block and canabalize the crank off of it for your engine.
2. Possibly, a good machine shop could fabricate, die (thread), and weld on a new "snout" on the end of your crank?
Either option will not be cheap!
**Edit: I have always thought that the threaded crank end appeared to be puny and weak. It "concerned" me every time I installed a Tecumseh flywheel and torqued down the flywheel nut to specs, that I could possible twist off the end of the crank in the process...
Michael