Bach English Suite - Duet using harpsichord music, by Ted Wolff
Bach's English Suites for harpsichord make great duets for vibes/marimba, vibes/piano, vibes/bass, or other combinations. The right hand and left hand are often just single lines and sound great when played on pretty much any instrument.
Arrangement is easy - vibes take the treble clef, marimba or piano take the bass clef. Manuscript is attached.