I will take a guess here and think you are after the shaft that the blade mounts to? I don't think one would be available new; it would be a matter of finding a junk machine. Whats wrong with the shaft you have? if its just the bearings they should be replaceable, it would be a matter of pressing them from the outer housing.
The only spare one I know of locally is at the tip off a later powertorque tilt a cut, the rest of the machine is gone, I only got the cowling from it before it was scrapped, said cowling went on Jeffreys edger.
