You could also take a length of all-ready black vinyl and fold over little sections, sewing seams on the back, making your own corrugation. It'll probably hold a curve more consistantly than cardboard. Maybe. Um, that's what I just did yesterday for some shoulder armor, and it worked for me.
As far as finding a pre-made mask like that, I've never seen one before, though. -_-* Did you ask in the general costume help forum?)