either,

Beat ruby weapon and get the desert rose i think its claaed, its desert something or other. Thats the hard one.

OR

Breed a good yellow chocobo with a great yellow chocobo using a carob nut to get either a green or blue chocobo. Then breed a green with a blue using a carob nut (i think). Then with your newly born black chocobo breed with it a wonderful yellow chocobo using a zeio nut (obtainable by beating the goblins north east of kalm) and you have yourself a gold chocobo. always save before you breed 2 chocobos then you wont have to wait a few years before you can breed them again.