I don't know where you could get songs with the bass track already muted, but I know how you could do this yourself.
Import your song(s) into Audacity or (perhaps better) Transcribe! then use the effects to mute the bass. In Audacity, you would use a high pass filter set to cut out the bass (say at 350 hz with 12 or 24 db). In Transcribe, there is a preset filter in the EQ section of the FX window that does this for you.
