You're right, Red-Coat. I'm not seeing a second source, either. "Head of a Savage" has a similar story, with the third one appearing in 1957, if I read it right. And this one, life mask/death mask self portrait, does suspiciously follow that same time line. And the "Head With Horns" multi million dollar fraud certainly points to big players, big auction houses, big money, and a situation where this original might be a fraud, also.
All the copies, and there are lots in all different materials, they would be copied after the "fraud", right ... do we see any appearing before, say 1957 ?
I can't really get a good grasp what is going on with it all. This mask looks more like it may have been tailored after "Head of a Savage" in an attempt to give it credibility ?
I'm amazed by how many copies are sold in such a large variety of materials. That's where OP's falls, I think ... a bronze resin cast ... generally accepted as copies of a Gauguin mask ... but, as you point out, there should be more of a verifiable trail for the original that this was copied from ?