I just got a call looking for a fan blade for a Dayton generator with a Fiat engine. I suspect this will be Generac but I don't know how you would look up parts on the Dayton side. Go through Grainger or what?
Start with Grainger's PN. If it is not too old they may have the info on it. The fan, probably did not come with the engine, so a Dayton PN is all there is. FWIW the PN for a fan for 4W117/18 with a Mazda TC engine is 57463. Good luck,