Where are the other shell-families on shellshows?

[Guest]

I have been visiting several shellshows in my life. As I am a Cowry and Cone-specialist myself, there is plenty for sale (if your wallet is thick enough....)Tables loaded with (sometimes very expensive) Cypraeidae and Conidae.
Closer inspection of the various tables show representatives from other well known families such as: Volutidae, Cassidae, Muricidae, Strombidae, Mitridae, etc.
But where are the others????
Good friends of mine are bivalve-specialists and hardly find anything (sometimes an expensive Spondylus or Pecten, but that's all...)
Where are families like: Tellina, Donax, Venus, Cardium, etc.?
In the gastropods you seldom encounter shells of families like:
Nerita, Columbella, Fissurella, Patella, Trochus, etc.