In The Division Weapon Skins are possibly the hardest to get mods for your gun. I’m not even sure they drop now since I haven’t gotten a single so far. They did drop in the Beta but it seems Ubisoft Massive changed things in the final release of The Division.
Today while randomly upgrading my wings I unlocked the Appearance Vendor and what do you know? He carries several Weapon Skins. The Appearance Vendor can be unlocked by purchasing the Supply Line upgrade for your Security Wing. The vendor will be located towards the very end of the base and shouldn’t be hard to find.
Like every vendor, the Appearance Vendor’s inventory will change every so often so keep checking for new skin designs.
Do note that these skins and other weapon mods are only visible to you, other players will only have the base gun visible to them.
The Division is now available on Xbox One, PC and PS4.