The previously rumored extension grip Z-GR1 and vertical bracket Z-VP1 for the new Nikon Z5 camera are already listed on the official Nikon store in Japan (Z-GR1, Z-VP1) but I cannot find them on the Nikon USA page or at Adorama and B&H. The Nikon Japan store also has new Nikon Z hot shoe covers. Additional photos of the new Z accessories:
Additional information can be found at DC.Watch (translation).
Pre-order links:
Nikon Z5: Adorama | B&H | FocusCamera | ParkCameras | WEX | Calumet
Nikon Z 24-50: Adorama| B&H | FocusCamera | ParkCameras | WEX | Calumet
Nikon Z TC: Adorama | B&H |FocusCamera | ParkCameras | WEX