Harmonix was swallowed up by Epic but they occasionally release "Fortnite Festival Guitars" which IIRC are compatible with Rock Band 4, and if you connect them

Harmonix was swallowed up by Epic but they occasionally release "Fortnite Festival Guitars" which IIRC are compatible with Rock Band 4, and if you connect them to a PC somehow they will also work with games like Clone Hero. For the legacy equipment, you're going to have to go thrifting and hope you find what you're looking for.