I don't know if you are still interested in this but here's some information:
The Commodore 64 had probably the best 8 bit sound and compositions for it's day. You may be able to get a few sid files (commodore 64 music) that are what you need. A good place to start is here:
Commodore 64 Music
The process would be:
1. Get a SID player
2. Download some music
3. Play the music through the sid player and convert it to WAV and save it to disk
4. Do what you need to the WAV for your game - convert it to MP3 or OGG, break it into smaller parts, etc.
If you want to try your hand at programming your own 8 bit SID tunes, you should check out Goat Tracker:
Goat Tracker
Enjoy your day.