There are a total of 10 bounties you need to kill. 5 can be found in Broken Valley and 5 in Orobas Fjords.
Broken Valley Map:
Hjalmar - Inside Number 2.1 on the western side
Hallorn - Inside the Derelict Tunnels (enter from any Number 2.8)
Yup'ik - Number 15
Jagon - Boss of the Bandits (inside Number 2.9)
Viper - Number 13
Orobas Fjords Map:
Barnabus - Inside Sinister Cavern (Number 5.3)
Alrik - Number 17
Moor - Number 16
Alutiiq - Inside Depleted Ore Mine (Number 5.7)
Ragon - Inside Dark Cave (Number 5.4)