Haruki Kadokawa Office (Kadokawa Haruki Jimusho) has posted 28 production stills from Jun'ya Satô's Yamato (Otoko-tachi no Yamato) on its website here. Raku Film (Rakueisha) has also posted a few stills on its website - three here (scroll 3/4 way down the page), and two there (again, scroll 3/4 way down the page). There are also several stills accompanying the official blog for the film. Finally, there's a short 'making of' doc here, although principal photography for the film only began on March 26 - which is why there's no footage from the film in the promo trailer. Incidentally, the budget for the film reportedly is ¥1.5 billion (approx. $14 million U.S.) - the same as the official production cost of Masaaki Tezuka's upcoming Civil War Self-Defense Forces 1549 (Sengoku jieitai 1549).
For more info on Yamato, see ScreenAnarchy's first article on it here, and the Internet Movie Database (IMDb) entry for it here.