Raphnet makes an adapter cable that converts a classic controller (Wii classic, Wii classic pro, NES classic, SNES classic) into a GameCube port. If you can't stomach paying $200 for the Hori
Wii Guitar / Classic Controller to USB Adapter for Clone Hero – DDRPad.com
How to use Almost Any Controller on the PlayStation Classic - YouTube
Wii Classic Controller to USB Joystick
Amazon.com: ELECOM Wii USB Adapter, Game Classic Controller / Classic Controller Pro to USB, Adapter for Windows PC for only one Player, 1m / 39 inch Length (JC-W01UWH) : Video Games
raphnet. - Classic controller to USB adapter - V2
Wireless Mod for Pro Classic Controller for the Wii : r/AskElectronics
raphnet. - News
Wii Mini Classic Controller CG Refurbished NOS New Old Stock - Etsy
Wii classic controller hack, now with more classic | Engadget
Wii Guitar / Classic Controller to USB Adapter for Clone Hero – DDRPad.com
raphnet. - Classic controller to USB adapter - V2
Wii Classic Controller to USB hack (compatible with SNES Classic controllers) : r/miniSNESmods