I do not buy full M5 stun guns, I craft them.
50 M5 stun gun salvage + 50 M3 carbanti salvage = 1 m5 stun gun.
I mean, you CAN buy a full gun but they cost 2541 crystals, there is one in my daily shipment right now.
As for the rest, you just have to buy them up a little at a time from guild store, guild event store, championship store, and shard store. For a long time I played by the rule that I never bought anything but g12 finishers (the upper left tile) from the championship store because that stuff is very hard to find. You can also buy gear bundles for real money in the data card store, but it does not go very far and then your grocery budget may suffer ...