IME, I've only seen them in Toronto, Canada, never in US either.
Some say they are too easily confused with the heavily protected Giant Mekong Catfish by the border officers and are mostly/too often not let through/confiscated. So exporters and importers stopped trying to bring them to the USA.
This story is a bit weak/hard to believe IMHO but IDK any better.
I am rather sure Wes Wong (fugupuff) or Rare Fish can bring you some.
Not rare in so california
There around just never when you want it. Sometimes you can't give these away!..
Tell us more, please, if you will.