Timing is most likely the key. If a dealer is 
offered something great (re: expensive) by 
his/her Japanese contact, then the dealer would 
be more likely to part with something from 
his/her collection; the dealer is, afterall, a 
collector like us.

There are a few dealers who put up wishlists, 
like Nick of Anime Chaos, but most likely they 
don't do so because they can get better results 
by giving their wishlists to their Japanese 
contacts instead of asking us, who often request 
them to help fulfill our wishlists.

---Trebuchet