Answer:
The Camo outfit comes from a random event called "Drill Demon". The Drill Sergeant will come pluck you out from wherever you are and make you do drills. He will give you a set of commands and if you follow them without fail or with little mistakes, you will be rewarded with a piece of clothing from the Camo outfit. There are three pieces - the hat, shirt, and the pants. After you get these pieces, you cannot get them again unless you lose them. If that's the case, then the next time you get conscripted by the Drill Demon, he will reward you with the missing piece. If you have all three pieces, you cannot get any more. He'll just give you some gp as a reward and tell you to, "Just take this and get out of my sight."