Youtuber Orvis25 suggested that I should make an addon for this mod so I made it :) Just put the gamedata file in your game file and done!
With this addon, all traders will buy your damaged weapons, even though it is completely broken!
It's time to raid the army bases and sell all the loots!
changelog 07/11/2018: Now using the optional file, traders will also sell you old ammo, which is cheaper! This is suggested by Orvis25 :)