Here is a descant for Thanksgiving. I am using it this Sunday at my church in a medley of Thanksgiving hymns we will all sing at the offertory, as follows;
#591 Come, Ye Thankful People Come, vs. 1
#589 Now Thank We All Our God, vs. 1, 3 (in E flat)
#590 We Gather Together, vs. 1
#591 Come, Ye Thankful People Come, vs. 4 with descant
Available in Key of F as well.
Almighty and gracious Father, we give you thanks for the fruits of the earth in their season and for the labors of those who harvest them. Make us, we pray, faithful stewards of your great bounty, for the provision of our necessities and the relief of all who are in need, to the glory of your Name; through Jesus Christ our Lord, who lives and reigns with you and the Holy Spirit, one God, now and for ever. Amen.
-The Book of Common Prayer, Collect for Thanksgiving Day