RetroGamingCable_UK sells 3 cables for the NGC right now :
CSYNC : slightly better than the other one (mostly for PVM/BVM users) : £21.59 + shipping
Sync-on-luma (RGsB) : very good and the cheapest : £17.99 + shipping
PAKAPUNCH (CSYNC) : the best choice, fully shielded, important if you want to use a SCART switcher : £27.59 = shipping
You seem to be listing the NTSC SNES cables. PAL Gamecube does not output CSYNC or Luma.
For Gamecube they only sell cables with composite video for sync or composite video+sync stripper. The latter should be avoided.