The Raphnet Wii Classic Controller to USB is the real del. It's seriously as good as a Wired Xbox 360 guitar. Legitimately buy one of these if you have a Wii Guitar.
raphnet. - SNES controller to USB adapter - V2
[raphnet] Classic Controller / Wii Guitar to USB adapter - V3 | eBay
raphnet. - Classic controller to USB adapter - V3
SNES Classic controller / Wii Guitar Clone Hero to USB adapter cable by raphnet – ASA College: Florida