Eve Engelbrite composed the music for Captain Bible. You can’t get any soundtrack files out of the game, but her personal website has hosted two original MIDIs for a number of years: the main theme (THEME.MID) and the Unibot theme (ROBOT.MID).
Check them out here:
Obviously how they sound will depend on the MIDI synthesizer you’re running, as illustrated in this interesting comparison by The Rec Room Plays.