I've been arranging some Christmas songs for 4 B-flat clarinets, or 4 of any of the same type of clarinet. Here is a list of these arrangements. Most of them are also available in versions for four violins (though in a different key than the clarinet arrangements.)
Away in a Manger (both of two commonly-used melodies for this song)
The Christmas Song (Chestnuts Roasting on an Open Fire)
Christmas Time Is Here (from "A Charlie Brown Christmas")
The First Noel
Four Carol Set (includes Huron Carol, See Amid the Winter's Snow, What Child is This? and It Came Upon the Midnight Clear)
Hark the Herald Angels Sing
Have Yourself a Merry Little Christmas
Joy To The World
Lo, How a Rose E'er Blooming
Sleigh Ride (Leroy Anderson)
Still, Still, Still
This list will be updated as I add more sheet music.
If you would like more sheet music for 4 clarinets, Robert Rainford has arranged some Christmas songs for 4 B-flat clarinets, with optional E-flat clarinet, alto clarinet, and bass clarinet parts. The book can be found here. This book contains an arrangement of "Silent Night" (different from my own arrangement,) as well as other Christmas songs.
More Christmas music for 4 clarinets can be found here, as well.