ok its been a little while since ive looked into this so bear with me,
if you want to use paint there is alumahyde and krylon paint i have seen people do some crazy camo paintjobs on ARs with this stuff
i like the look of parkerizing personally, and its more durable than any kind of paint
http://en.wikipedia.org/wiki/Parkerize
you can buy little kits of the chemicals and do it yourself, i have no idea how difficult it is or how much it costs
hopefully that can get your started