I'd like to have access to the rare weapons in both the quick match as well as the campaign, I've figured out how to import a few, however others for some reason don't want to work. I also have no idea really how to make the accessible in the campaign outside of reclaiming them from the battlefield.

Off the top of my head, accessibility of a weapon in an armory is determined by a few things:
* the weapon needs to be loaded, i.e. listed in all_weapons.xml for quickmatches or invasion_all_weapon.xml for campaign
* in_stock value needs to be 1 in the weapon's commonness tag
* the weapon needs to be among the faction resources, for the default soldier group specifically to be shown players, e.g. in green_primaries.resources or elsewhere.

By default e.g. green.xml includes these resources for the default soldier group


Which weapons do you have trouble enabling with?

So I have been having similar problems, I have been able to add the p90, barret, f200, vss, n2000, aa12, and desert eagle to the armory both for quick matches and campaign, but there are a few weapons that haven't been working. Like the fn-fal, m16lsw, hk417, bizon, and aug. I was thinking that they are either not implemented in the actual game, or I am doing something completely wrong/ forgetting something.

All of the ones you listed that aren't in the game, actually aren't in the game. Your intuition was correct.

Thank you

I can get some weapons to actually work, but not others. For example, the m712 pistol works, and I can get it to show up in the armory, but a weapon like the MG42 doesn't, no matter what I do. Fiddle with invasion_all_weapons.xml, the weapon's file itself, the faction primary lists... What gives, man?