You can already preorder the Sony A9 at Amazon US (Click here)!
You can also preorder the new 100-400mm FE GM lens at Amazon (Click here).
Also the A9 accessories are available for preorder now:
Sony A9 battery grip at Amazon.
Sony A9 Glass screen protector at Amazon.
NP-FZ100 battery for the A9 at Amazon.
GP-EX1 grip at Amazon.
MQZ1 multi battery charger at Amazon.
BCQZ1 Z-series Battery Charger at Amazon.
UPDATE: Also in Germany and UK you can preorder the camera:
Sony A9 at Calumet.de, Park UK, Jessops. Wex UK.
Sony 100-400mm at Calumet.de. Park UK, Jessops and Wex UK.
Sony A9 battery grip at Wex UK. Jessops.
GP-EX1 grip at Wex UK.
MQZ1 multi battery charger at Wex UK.