I thought that, but dont have a lathe...
the main part of the shaft is 5/8", I found some 10T sprockets for a #35 chain on McMaster for that size, was thinking of just cutting off the threaded part and possibly welding the sprocket to the main part of the shaft or grinding it down on one side to make it a D shaped shaft...
I tried to find a threaded sprocket, but dont think they exist..