Which experts welcome correspondence?
Very few, sadly. The more one learns about a particular family, the more
time each new piece of research takes. Most true experts have their hands
full staying ahead of the game; if they took up even a fraction of the
correspondence they receive asking for help with this and that or proposing
collaborative projects and so on, they'd soon fall behind. Think how easy
it must have been to be an expert on the Muricidae or Buccinidae a mere 50
years ago, compared to the same task now.

Which ones are on THIS
> list?
It thus stands to reason that anyone who is an expert is likely to keep
quiet about it.