Vacuum forming might also be an option (as was mentioned), but unfortunately a sample might need to be destroyed in order to create a mold. Probably not practical, unless you can model it. Vacuum forming might back-light better than 3D-printing (parallel lines might show), as lots of folks like to have the eye's illuminated on the head.

I have a complete head, but it's a bit warped from heat. Horns are sagging down a bit more than they should. Need to see if it's possible to reheat and warp back they way it should be.