I went to the Corsair's channel SE of Skull Island looking for Scaramanga and Corsair's cove. I don't see it. Where can Scaramanga be found?
Your quest arrow should take you right to it. Just dock your ship at that island in Corsair's cove and look around. I do believe it was lying on the ground near some washed up wreckage. When you get near it a text box will pop up and ask you to press the letter 'X' to pick it up. Go into your quest log and click on that quest. Hit the letter 'Q' to open it. Then the arrow should show you the way.