All of the classified items in Black Ops III (including the classified weapons) are obtained through the Black Market in Multiplayer as a random drop.

How do you access the Black Market in Black Ops 3?

The Black Market is a feature in Call of Duty: Black Ops III in multiplayer. The Black Market is where the player can exchange Cryptokeys for Supply Drops. It can be accessed through the Public Match Multiplayer menu.

How do you unlock hero gear?

All Specialist Challenges to Get Hero Gear in Call of Duty Black Ops 3
Firebreak Body: Kill 4 enemies stunned by your heat wave in a single match.Firebreak Helmet: Kill 6 enemies with the Purifier in a single game.Reaper Body: Kill 4 enemies while Psychosis is active.