Z, why not take any MIDI BiaB song and either in BiaB or the DAW of your choice and lower the notes an octave or two? You can have BiaB generate a melody for you as well that you can drop an octave. Then either read or print it using only the bass clef.

A plus to this is that you already have the backing tracks made for you. For instance generate a song with a melody, drop the melody an octave or two, and print it. Then mute the melody, have the other tracks play at their original octave, and play the leads. Or drop the piano track to the bass clef and play it. There are lots of options like this when you use MIDI.

Whenever I get something stuck in the back of my throat, I dislodge it by drinking a beer.
It's called the Heineken Maneuver.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware