Thanks Martha and Ken! I do some research into these options.
Dulcimer Duet or Dulcimer/Fiddle Duet songbooks?
I'm really enjoying Heidi Muller's new "Dulcimer Duos" book. It has some beautiful arrangements (some of my favorites are Leaving the Methow, An Afternoon at Cohan's, Winter's Turning, and Do You Love an Apple).
Nina Zanetti's "Tunes for Two or More" volumes 1, 2, and 3 also have beautiful multi-part arrangements.
These are all for dulcimers:
Sue Carpenter's Joined in Harmony book
Larry Conger Christmas Duets
There are many other Larry Conger arrangements on his website with two parts
Many of Linda Brockington's dulcimer books have two or even three part arrangements
Tull Glazener - many of his arrangements have multiple parts