First go and get a helicopter, then go to the mision in Rebadeaux, Redlight district.

Land the helicopter and go to the mission. When the mission starts get in the helicopter you brought with you and find the Sons of Samedi Oppressor.

When you have found it on the roof press down twice and it will say mission failed, then after that press B to exit the mission.

The Sons of Samedi Oppressor will be there and you can store it at your garage.