There are five basic Amigos available in the game. To get two more, K-9000 and Champagne, you need to buy the corresponding DLC (available in the Ultimate version).
Amigos
Locations on Yara
1
Boom Boom
Reward for completing "Boom or Bust" Yaran story. You can also find him without needing to accept the quest. Dog is trapped inside a blue shipping container. Just shoot off the lock of this shipping container.
2Chicharrón
You will get it after you complete three Yaran storries: "Man's Best Enemy", "Pecking Order", and finally "Wingman".
3Chorizo
You will get it after you complete two Yaran storries: Who's a Good Boy? and Fetch Quest.
4Guapo
You will recieve it automatically during the "Juan Of A Kind" operation.
5Oluso
Reward for completing "Triada Blessings" Yaran story.