Hi Lianyi and welcome to the forum.
I can't add too much more to what Nick and Sonny have already said, the cross you posted is a Souval and a very expensive example at that!
Klaus Butschek is a good and reputable dealer, you could also try Carsten Baldes, Thomas Huss, Helmut Weitze or Kai Winkler. Try a Google search for these names and you'll find their websites easily.
Looking for LDO marked EK2s and items relating to U-406.....