You're unlikely to find many good leadsheets for rock and pop because it's rare that there are keyboard leads. You'll get the odd keyboard riff in a song that really stands out, but not enough to warrant a full part. And since keyboard players in a band are never playing the melody all the way through (i.e. doubling the vocals, doubling the guitar solo, etc.) there isn't as much sheet music that has that kind of thing. Certainly, you can go buy a book of, say, Nirvana songs arranged for piano, but they always sound really cheesy.
Honestly, your best bet is to teach yourself to pick things up by ear, using the chord chart as an example. If you're playing on your own, work out a part with melody from that, and if you're playing with a band, think about how you fit in with what they're playing.