Bwing! Here I am!
Yup, when I was going over the ref pics in the planning stages of my helmet, I was convinced that I had seen that shape before. Then it hit me; a GI steelpot helmet.
It's well known that the SW prop and costume departments used alot of surplus military junk. If they didn't exactly use a helmet itself, I would think it would be a fair assumption that a helmet was used as a master to pull a crown from.
Just my two cents, but if you look through the helmet archives, you'll see some of my posts, pics, and links to my helmet building odyssey.
Good luck.