I noticed that true M. auratus aren't so common anymore, but the "dwarf auratus" shows up disappointingly often.
Really nice M. estherae "Red Zebra" aren't very common anymore. The prices on the ones that do show up seem to have sharply risen as well! (You know who you are ...

)
High quality L. caeruleus were hard to find for a while, but I believe they are trending up.
P. electra used to be really common in the area, but are less so now.
A lot of stuff is cyclic though because it's market driven.