Most people know this traditional Thanksgiving Hymn as "Come, Ye Thankful People, Come," but the piece was originally called "St. George's, Windsor," and was written by Sir George Job Elvey (1816-1893) who was the organist there. It works very well as a duet for violin and viola.
You can click on the images for a larger view, and a PDF will soon be available on this page of the IMSLP.
Here's a special bonus for your Thanksgiving enjoyment that can be played on any combination of instruments: "We Gather Together to ask the Lord's Blessing."
You can get a PDF here.