There are currently two ways to unlock this weapon;
One way to obtain it is by purchasing it through the store when available.
The other way of obtaining it is by finding The Chemist located within the Radiation Area of the DMZ.
- It’s recommended you have a gas mask before heading into the radiated area.
As soon as you enter the area, his locate will be pinged on the map, you’ll then want to quickly locate and kill him, forcing him to drop the M13B contraband weapon but be careful as the area is swarmed with ads safeguarding him.
From here, all you have to do is head for an Exfil point and safely extract.