Work in Progess
Finish your first BANDIDOS mission.
This is your reward.
In the Mission "FUEL THE REVOLUTION" you have to find and kill a target at Vencejo, Isla Santuario.
This target carries the key for the FND Munitions Storage.
Of the 3 camps, it's in the one in the middle.
Enter the bunker and you can climb down the ladder to open the Storage.
The weapon is inside.
At GOLFO VASTO LIGHTHOUSE, BALACERAS
Grapple up the lighthouse. The chest is at the top.