This idea has been mentioned many times before, but I don't think it got the proper attention. I think having Gun Camos would be something to work for. There could be a certain ammount of pks or spars needed for a camo. For example the first camo could be 100K pks or 10k spar wins, then the next 200K pks or 20k spar wins, 300k or 30k spar wins, and so on. Remember we need the ammount of pks or spar wins to be relatively high so that the camos can be rare and shows off someone's hard work. They would be like pk and spar hats, not everyone has them and they are relatively uncommon.
The second option would be to make them more common like 10k pks or 1k spar wins, 25k pks or 2.5k spar wins, and so on. There would need to be alot more camos if this way was to be chosen though.
Credit to Vince for helping me comeup with the idea along time ago and Street for bringing it back up to attention.