The new Tamron 150-500mm f/5-6.7 Di III VC VXD lens for Nikon Z-mount (Model A057) is now shipping and is currently in stock at B&H Photo:
Check also availability at Adorama, Calumet, Erhardt, Koch, WEX, and Park.
Additional information on the new lens can be found here:
Tamron 150-500mm f/5-6.7 DI III VC VXD lens for Nikon Z-mount officially announced