There were two books released at comic market 82 related to symphogear. First the character designer, Satoshi Koike released a "sketchbook" which basically consists of sketches he did for various series that he worked on. The book isn't entirely dedicated to Symphogear, nor is it in color, but it does have a lot of the sketches he posted on twitter printed in a higher quality (such as Chris wearing the Lydian school outfit and the festival group picture which can be seen on the cover of the book). You can samples of the included sketches in the image above.
Koike also included a fan with some colored art for those lucky enough to be at the event.
The second book was released by the action director, Fumiaki Kouta, entitled "Highlight book 8" which is the 8th book in the "Highlight" series that he's released. This book isn't entirely dedicated to Symphogear either, but it contains a rare look at the production side of things by not only including sketches, but also storyboards for the action sequences.
Now the unfortunate part of these releases is that they are printed in limited qualities and unless you were there, chances are you're not going to be able to find one anywhere. I stalked Yahoo Japan for weeks after I found out about them and only managed to snag Koike's sketchbook (and even then at a pretty high price!). In the past month or so I've watched the auctions every day and so far Kouta's Highlight book hasn't shown up and even if it does, I imagine it would be going for a price well out of my range. Fortunately, pictures of the content do exist.
Take a look below:
I doubt we'll ever get proper scans of these books as they are pretty rare and their owners likely want to keep them in good condition, I might see what I can do with scanning Koike's sketchbook when it arrives but I don't want to ruin it either! In the meantime, I hope for a more thorough official artbook release - or maybe some more books at winter comiket!