Well, not just rock & roll, but also jazz and blues. And - although some people might object to this - there's no reason why you can't try playing some of your classical repertoire on these instruments. I think anything that would have been played on a harpsichord, clavichord or fortepiano would work quite nicely. So, J.S. Bach, Handel, Scarlatti, Clementi... If you enjoy it and it works for you, it's not wrong! Also there are plenty of pop-style contemporary classical pieces by composers such as Christopher Norton which should work very well on the electrics. I don't know if there are many good quality free scores available, because of copyright, but there are a lot of MIDI files around. I'm not sure where you'd get some good quality rock MIDI files, but the Pianoteq demo by Piet de Ridder (available to download here https://forum.modartt.com/uploads.php ) is an excellent starting point for blues style.