TTX Tech GameCube Controller Adapter for Wii U and Switch - Micro Center
4 Port For Gamecube Controller Adapter For Nintendo Switch/wii U/pc Usb Adapter - Buy Controler Adapter For Wii U,For Gamecube Controller Adapter For Nintendo Switch/wii U/pc Usb Adapter Controller Adapter,Gc Controller Adapter
You can use the Smash Brothers Gamecube adapter in portable mode with a USB C adapter (Rumble works too) : r/NintendoSwitch