I do know the golden wrench shares the model with the wrench. However its more than just a reskin. From what I understand its basically an "attribute" placed on the wrench to give it its golden look. This condition can be placed on any other model in source. Such as when you kill someone with the wrench, source applies this attribute to their bodies.
I dont know how the hell your supposed to apply this in hammer, but i hope this helps narrow it down. I think it may have been a beta for paint...