You can make one pretty easily without a pattern. Just measure his neck and add a couple inches to that measurement to make it scrunch a bit. Then make a swatch our of your yarn in the stitch of your choice, and then cast on for your project. (i.e. If you get 5 sts per inch on your swatch, and you want your piece to be 6 inches high, then CO 30)
Then knit until it is long enough to go around his neck, and then seam up the ends to make a tube.
There ya go...a neckwarmer.