Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:5877700.
Here's a really old file i made of rex's helmet. It's not very accurate, but i had it laying around so figured why not post it. Just use the exploded image for the placement of all the details, you'll need 2 ear greebles and one chin detail. I scaled up the files to 550% for my head, but you defiantly want to check fitment for yourself.
be sure to post a make and check out my other files