How to Use a Gamecube Controller on a Wii: 5 Steps (with Pictures)
GameCube Controller Adapter for Wii U, Nintendo Switch and PC USB – Lexuma
Amazon.com: Mayflash GameCube Controller Adapter for Wii & Wii U (Dual Pack), White : Video Games
Amazon.com: FIOTOK Gamecube Controller, Classic Wired Controller for Wii Nintendo Gamecube (Black) : Video Games
Wii U can use two GameCube controller adapters
How to Connect a GameCube Controller to the Wii - Howchoo
Just Got One of Those Gamecube Controllers That Plug Into the Wii Remote. What's the Difference Between These and the Actual Gamecube Controllers? : r/smashbros