If you are looking for a component cable that can be used on standard A/V port rather than digital port you won't find one. It cannot be done as GameCube standard A/V port does not have pinout for Pb & Pr. You can get RGB, S-Video, or composite video out of it but not component (Y/Pb/Pr).
Either you buy a composite to component signal converter or find the first GameCube model (DOL-101) and use Nintendo's component cable.