In order to acquire Mayan Outfit, which deflects metal projectiles, you have to find 16 Mayan Stelas and arrange Mayan Stones in correct order. Mayan Stelas are scattered throughout the map, usually one per island (Cape Bonavista, Cat Island, Great Inagua, Tulum, Tortuga, Matanzas, New Bone and Long Bay), but on some islands you can find two Stelas: Pinos Isle, Misteriosa, Santanillas and Isla Providencia.
In order to reach Isla Providencia and Long Bay Islands you should progress through your main story.
When you find a Mayan Stela, you have to solve a puzzle and reveal stones that each Stela hides. The Mayan Outfit is hidden behind a secret door in Tulum, that can be opened after collecting 16 Mayan Stones. When you finish the mission The Memory 04 Overrun and Outnumbered, talk to James Kidd, who will unveil a hidden location of Mayan Outfit.
1. Cape Bonavista Mayan Stone
2. Cat Island Mayan Stone
3. Great Inagua Mayan Stone
Note: Mission “This Old Cove”, where you follow James Kidd takes you to this location. Finding this Mayan Stone is part of the mission.