I had to move to Panama to catch, and get a couple of the fish I wanted, because, at least when I left the U.S., none were available.

Darienheros calobrense above, Isthmoheros tuyrense below

But I think almost more rare, are Iranocichla hormuzensis from southern Iran, and Nandopsis ramsdeni from a small region in Cuba.
These both are geopolitically almost impossible for a U.S. citizen to get
Although I have heard a collector (named Max, a former Russian citizen(?)) has been allowed to go to Cuba to get some N ramsdeni.
I wonder though, what does rare mean?
Not found in LFSs.........only coming from a tiny geographic area, or one tiny lake, or pool?
Like the desert pupfish in the western US, or Alcolapia in lake Natron in Africa, saltier than the ocean?
I must admit I stopped buying from LDSs almost 20 years ago, because they never carried anything I wanted, and I found it was very hard to trust that they even knew the proper names of fish, and tell them apart.