It's a special cord that is made only by Rocksmith. (I've used Rocksmith for several years now)
Based on the Rocksmith forum, I think this might work for you:
https://www.amazon.com/Wired-Control.../dp/B0055464UQ
And if you didnt already know this - if you're playing Rocksmith on your computer, there are mods that allow you to play just about any song you've ever wanted to play.
hit me up if you want that info...