You can't get Baltic Birch plywood in Norway? It's imported into the U.S.A. from Scandinavia, where the world's supply comes from! I'm half Norwegian myself (surname Jerde), my great-great grandfather immigrating in the 19th century to Minnesota, then onto South Dakoda.
There are two products great for constrained-layer damping: EAR IsoDamp (Kait doesn't like it though) and WallDamp by Acoustic Science Corp. (the Tube Trap company). And of course Sorbothane. A layer of any of them between two pieces of very stiff material makes for a great shelf.
I have no experience with Shun Mook, that whole concept of which I am dubious.