If you preordered Original Generations 2, chances are you received a ‘digest book’ of sorts, detailing the various mecha in the game as well, such as a comic, and random doujinshi ads. If you did miss out though, you’re in luck, because a kind soul on the Interwebs has managed to scan and upload the entire thing.
The download link for the file is here. The file is passworded but you can find the password itself on the comments if you open it with WinRAR.