Becky and Ernie Brock at Arriere-Cour productions have several very nice books of flute and harp music, all arranged for lever harp.
For a harp/piano duet, Les Pins de Charlannes by Renie is pretty, simple piece.
Offhand I can’t think of any arrangements of the swan as a duo with lever harp (if you can do the levers in the harp part, you’re usually advanced enough not to need an arrangement). There are a few solo arrangements for lever harp (including mine, but it’s pretty tricky–the others are easier).