The Chocobo Sage is a person that is devoted to Chocobos and knows a lot about them. You can locate the Sage's house directly east of Icicle Inn. It's a small house surrounded by mountains. You'll need the Highwind to reach it. He'll be able to sell you the highest quality and rarest nuts and greens available in the game.

Check out his Chocobo in the stall, it'll spit out a Enemy Skill Materia just for you.