Azerone just put them up for sale on amazon:
I can vouch for this seller, I have 12 of those panels ( http://marc.merlins.org/perso/arduino/post_2020-03-13_RGB-Panels_-from-192x80_-to-384x192_-to-384x256-and-maybe-not-much-beyond.html ).
For full disclosure, the pixels come off easily in shipping. Azerone has worked with me in finding ways to ship those panels without pixels coming off during the long trip (2 weeks).
As a reminder, you can only expect to run a single one of those with SmartMatrix (and you’ll need the FM6126A init hack). If you want more than one, you’ll need to use rPi but with my glue driver, you can still run your arduino code on rPi, so it’s not too bad as long as you don’t rely on other GPIO drivers ( see http://marc.merlins.org/perso/arduino/post_2020-01-01_Running-FastLED_-Adafruit_GFX_-and-LEDMatrix-code-on-High-Resolution-RGBPanels-with-a-Raspberry-Pi.html )