Okay, you know the eastern exit in Ozmone Plains to the Golmore Jungle? If you go west and south from there, you'll enter a place with a twisting serpentine path. There's a fixed chance that a Garif Hunter will be wandering around in there. If you cast any spell on him (even healing) he'll turn hostile and attack you.

BTW, you don't have to get the full quota of monsters to get the icon in the sky Pirate's Den. Just one of each. You do, however, get extra information.