If you come up empty for an actual Datsun pulley, look for an old school British resto shop in your area (wherever that is), cuz many of the early Datsun parts were basically licensed/copied from British engineering by Datsun.  I worked in the British parts industry for years.  Is that a cast pulley?  I don't remember the British counterpart being cast, but if the same engineering design in stamped steel, one might work......?  There might be a "spacer" behind your pulley (the British DID have a spacer), so if you find a British pulley that fits the shaft but rubs on the generator itself, look into spacing it out with a deeper spacer.  Good luck with your search!