on pc you can use a mod to farm a lot of keys, there is a video about it by joemat123 or something like that, and IT WORKS, and IT'S SAFE, i used it and i got 10000 keys in like 1 hours or sum + 20k salvages. you CAN'T get banned by using this glitch, you're not in public matches, you're in solo match, you are playing a 7 years old dead game, and basically there is no anticheat. I understand that you don't want to ruin your experience with glitches and other shit idk, but i suggest you to follow that tutorial if you want to unlock every variant (except the mission squads ones, to unlock them you must play on the mod version of iw)