I am a seamstress, so maybe I can help you. It can be made simply. I don't think there is a pattern, as there are so many styles of cases ---as well as many sizes and shapes of dulcimers. I have made my own cases. I measure the dulcimer and make a rectangular case to fit the measurements (with some ease). Remember that the case has to fit around the thickness of the dulcimer, not just the length and width. So allow for that. If you are experienced at sewing, you may want to box the sides. Use some quilt batting between the outer layer and the inner layer, to pad the case. You may want to put a layer of a waterproof fabric in there too, since we go to so many jams where it may rain or be damp. You can use any fabric, even an old quilt. I saw a case made out of a blue jean leg (crude, but functional). Make a closure from velcro, zipper, etc. Make some backpack straps, or take some from an old backpack. I also like a large pocket for my music book, a couple of small pockets for the tuner, capo, picks, etc., and a place for a pencil. Velcro closes these securely. Making your own "custom" case is fun and it will be exactly the way you want it.