i too have been pondering making my own AoT mask. partly for airsoft and also just to hang up in my office, hopefully next to my mando helmet and bat-cowl someday.
if purchasing is an option, here are two options.
http://www.cactushobbies.com/news2.html
http://www.arctactical.com/cp/salemmask.html
I also saw a few reproductions on ebay. give that a look.
If you would like to make your own:
(please forgive my typing if it doesnt seem clear,.. havent slept in 2 days. kinda burnt out from playin rainbow6 nonstop and shotgunning mt. dew. lol )
i've been planning it starting with a standard mylex hockey mask or a standard airsoft mask. both will take a beating and still protect your face. If you go with the hockey mask idea, you'll need to use some 22 guage wire mesh, some shatter resistant plexiglass, or shooting glasses lenses to cover the eyes for protection.
using pieces of plastic or carboard, you could flesh out "wraparound" parts of the mask on the sides and top of the mask. At this point, you'd have the "frame" of your mask.
starting with your mask of choice as a base turned frame, you COULD use layers of plaster of paris OR fiberglass resin with gauze to build up the shape of the mask face. add the brow, nose, whatever. apply it a layer at a time, going slowly until you have the shape your looking for. after its set, slap on a coat of fiberglass resin to all surfaces, sand lightly, paint, put some padding on the inside and give it a few test fires while wrapped around a balloon.
i dont know if that would work. and it would take a lot of elbow grease, but it might just do the trick. im too obsessed with my Mando and ghostbuster suits to begin another project yet.
i figured thats what i would try after seeing this homemade mask and reading some comments on airsoft forums from other people making their own masks. it looks like an airsoft mask with the bridge of the nose and the brow sculpted on.
good luck