These were offered up a little while ago... gone now, sound rare to the hobby... Nematobrycon lacortei

[Magnum Man]

keeping an eye out if they come around again...

don't know how good a source this is, but it came up 1st in my search...

Rainbow Tetra (Nematobrycon lacortei): Ultimate Care Guide - Fish Laboratory

Rainbow Tetra, Nematobrycon lacortei, are rarely seen in the aquarium hobby. They are beautiful, hardy fish, but they need expert care. They are tropical

www.fishlaboratory.com

and my old stand by...

Nematobrycon lacortei – Rainbow Tetra — Seriously Fish

www.seriouslyfish.com

 

[GaryE]

They are what I call once a year tetras - they show up, but you are lucky to find one import per annum. So they aren't rare, but they are uncommon.
I also find when they are listed, what arrives are often not lacortei. They're often the more available palmeri.

 

[jaylach]

Found them on Dan's Fish but.... out of stock.