It does say "Custom," so he/she could've made it themselves.
I know you guys like to see odd Ebay listings... And I found this odd gem:
Is this thing legit? I mean where could he/she have gotten it?
Yea, it is said in listing description that it is custom mask. I'm pretty sure that it comes from shapeways:
Mask in auction is 18k gold which is available on shapeways and that custom axle on back of mask and also not 100% mapping to original says that it was probably 3D designed and printed.