They are, indeed, motorcycle helmets with a plastic 'face' piece glued to them. I have a Wing Commander III/IV helmet and can take pictures if needed (there are various other little details, too, but nothing outrageous--like a metal nameplate affixed to the back).
I know the Star Wars fandom is very into casting Stormtrooper armor, so maybe that's something we could look into. I would certainly be happy to let someone come take a mold of my prop if it meant we could make helmet kits for everyone--but I have no idea where you start with something like that! I'm thinking with a single piece it probably isn't that expensive, we just need someone with the know-how to do it.