To make a visor, you can use any plastic sheet that is transparent or translucent. Plastic sheets come in many colors but be careful if you buy one. The foam files for the Armor from halo infinite have the visor pattern on the foam files. Use that to trace on the plastic. You would then need a saw of some sort to cut the plastic. Then, use mirror spray on the inside to make the outside of the visor to give it the mirror effect.
Or you can vaccum form a visor, which I don't really know how to do