Greetings —
I’ve been looking for a good (read cheap) way to store and carry whistles safely. At the risk of mentioning something you all know about, I recently bought some finger & toe bandage by Softeze. It comes in a 36" roll, has a gauze liner and foam outer surface and can be cut to length. One roll of 3/4" diameter (Medium) size (at about $ 8.50) provides protection for 3 D whistles. It also comes in 5/8" (small) and 1" (large) diameters.
You can buy it on line in lots of places; e.g., Amazon or www.comforthouse.com/foambanforfi.html but you might try a local medical supply store to avoid significant shipping charges.
Best wishes.
Steve