As far as vacuum forming, you can check you local area for manufacturers that vacuum form and do part prototyping. Thats how I got my 1st version of my Strider helmet's visor, which is also like domed like the EVA. You can print out the shape of the buck you need and then work with them to get done. You may need to cast it in a heat resistant plaster like Ultracal 30 gypsum cement.