Besides the card from Sapphire that is mentioned in the tweet, Newegg also has a PowerColor card for $399.99 and a Gigabyte version for $409.99. Good to see prices finally come down to more normal levels!
Still no word about custom cards though.
Radeon #RXVega 56 is in stock at $399. Get it now! https://t.co/kiCj0EDL5r pic.twitter.com/v8N2R677rx
— Radeon RX (@Radeon) November 8, 2017