you dont extract alpha maps, they come in the original textures. if you're using photoshop, just open the regular armor texture and under your layers palette (F7) click channels. select the alpha channel and hit CTRL+A, CTRL+C, CTRL+SHIFT+~, CTRL+V, then CTRL+E to merge it.
all that does is copy your alpha and paste it over your regular texture. then just save it as whatever you want
