Project Nemesis is a fan driven website for games that use the One-Roll Engine (like Nemesis, Wild Talents, Reign and Monsters) or Chaosium's Basic Roleplay System (BRP) (like Call of Cthulhu) and the Delta Green setting.
Something I've learned in the military is that the good ole' days of weapons "falling off the back of a truck" or taking of war souveniers is largely gone.
The powers that be keep a pretty tight leash on weapons and other high-tech gear. If you really want to have access to this sort of stuff it is better to do either a hybrid op or one where official cover can be used. Then your cell can play with the toys.
As for keeping the Green Boxes full, some alternatives ways I've used during Ops are:
1) Covert Operations Logistics. Those wonderful operations run by the CIA and others to supply third world governments and insurgents are great for diverting resources with a few friendlies/agents in the right place. They are notorious for being lax in how the resources are gotten and who they go to and in some cases are untraceable because of being "deniable" in the first place. While you won't get cutting edge material, you can still pick up a few toys without anyone noticing.
2) Weapon Buy-Back Programs/Evidence Destruction. Pay a few underpaid and corrupt civil officials that are supposed to be destroying evidence/weapons after they are done with them to let a few fall into your hands. Anybody gets wise and you set them up with a "sting operation" to make the whole thing look legit. Again, you won't get cutting edge stuff usually but it allows you some variety in what you put in a Green Box. Agents might find some old Saturday Night Specials or the latest in submachine guns.
3) Drug Evidence Seizure Auctions. Again, a few agents in the right places might be able to either take items that have been seized by drug dealers and placed up for auction or rig an auction so that DG gets the assets. Great way to get vehicles and safehouses.
4) Legitimate Arms Dealers. Many arms dealers/companies will provide samples of new items free to the military to try and get contracts. Some of these might make their way to a green box. Of course, this is part of what got Rogue Warrior Marchinko into trouble...
5) Crime. This is definitely depending on one's personal taste. This could be anything from accepting bribes to turn a blind eye to agents setting up criminals to steal their stashes for ops to more institutionalized criminal activities of the Iran-Contra or Mena Airport Connection kinda variety. Depending on how much outside material you want to mix into your monster bashing, this sorts of crimes and conspiracies can provide interesting diversions for your agents.