Purchase high-powered weaponry, attachments and items.
Civilian Level unlock
The Rebel Black Market is the place to be. There's guns, ammo, attachments and other miscellaneous items you can't get anywhere else as a regular Civilian. Although it sounds amazing, those Rebels are fighting a war... the weapons you buy there could be extremely overpriced.
A similar shop is also unlocked through the Civilian level which is at every regular Gun shop. You will eventually get the option to buy illegal weapons under the counter from Gun shop owners depending on their stock. Sometimes though, the guns they're selling illegally are just regular pistols with erased serial numbers.