I've found a few extra large versions of the last few promo images floating around the web.

Kokuhaku
3769x2691

Last Love Letter
1654x1098

Somaruyo
2050x1375
The Kokuhaku and Somaruyo ones are extra interesting because they still include all the metadata included by the camera when the pictures were taken. This can tell us things like:
-The camera used is the ($2,400 USD)
Nikon D700.
-The Kokuhaku picture was taken on December 15, 2008 and the Somaruyo picture was taken on August 27, 2008.
-The editing software used is Adobe Photoshop CS2 Macintosh.
-The Kokuhaku picture includes a link to a resource on
image.net, Getty Image's media-only outlet; as well as a username (either the owner of the image or the one that downloaded it, I guess) I wish I had a contact with an image.net account!
There's a bunch of other technical info about the pictures included as well, like exposure time and aperture. (Which are interesting only to the photographer types like me, of course!

)
Anyway, I'll keep looking and see if I can't find more images like this. They do make for such good posters! [Image of my printouts to come]