Signed up just to say I'm fairly certain the "armour plate" is the shell from a skate style helmet with part of it trimmed out and the inner foam removed.
I definitely agree. Looking into it a bit more it looks like this helmet may be the base for it or something like this helmet.
View attachment 669864 View attachment 669863
It called the Pro Tec Ace, the holes on the rebel helmet look a bit more rectangular but it's a really good start.
There is something about this helmet that's making me giddy inside. That being said, in an effort to find as much reference as possible, I've come across some things that may be of help:
Helmet on figure in bottom left
View attachment 669909
Various screenshots taken from 2 trailers and Celebration reel:
View attachment 669919 View attachment 669918 View attachment 669917 View attachment 669916 View attachment 669915 View attachment 669914 View attachment 669913 View attachment 669912 View attachment 669920