Thanks for providing the pics above! Those help a ton! So you need the hollow/removable helmets? I'm gonna make a mold of this helmet, then. Or would you rather dremel out a cast based on ROTS #41 Clone Trooper? That one might be too small for the clone heads, though.
Talking about
Clonehead - he might have some of those in stock and ready to ship already!
Just shoot him a message to ask!