I've been coveting this gorgeous Russian military map case, which Gizmodo acquired and posted in an article about using military map cases to hold iPads:
But yeah, good luck finding one! They also had some shots of map cases that seemed cool until you realized they were WWII Nazi issue, which made me a little queasy.
Since then I've been on the lookout for a more recent military-style, iPad-sized bag. I came across the awesome-looking Remora bag, from California-based Maxpedition.
Across an actual back, the bag is smaller than it looks in the hero shots, as you can see below, and at 9" x 7" the main compartment is too small to hold an iPad.
Still, a cool bag nonetheless; I dig the copious pockets and the fact that there are multiple attachment points, so you can put a strap where you want it, adjusting the angle of hang to your taste (rendering quicker access for a camera, for instance).
The Remora is part of their Gearslinger line, which vary in size and capacity, but all have similar style:
Bag lovers and designers should check out the rest of Maxpedition's prolific selection; you could literally spend hours combing through their hundreds of military-inspired designs of all types.