All purchasing options available here:
http://www.ak47catalog.com

I recommend the complete 14-volume set in electronic format:
https://www.lulu.com/shop/rob-stott/the-ak47-catalog-volume-1-14/ebook/product-2g8epy.html?page=1&pageSize=4

Rob Stott is an AK subject matter expert who has been producing The AK47 Catalog since 2013. He travels to various museums, factories, and private collections finding and photographing different AK variants and then prints those as a photo catalog. Each volume is approximately 80 pages, and the most recent release was Volume 14. There is (intentionally) almost no text; just photographs and a few minimal supporting notes.

As photographic reference material, the Catalog is a nice valuable piece of material. For differentiating between specific sub-variants, is it quite useful, and it is a great resource for clone rifle builders. What I do not like is the lack of unified organization and the price. Each volume is $28 printed softcover, because they are made as print-on-demand items through Lulu (possibly the most expensive and least efficient way to print one book, much less 14 of them). Total cost to purchase a complete set is something like $400 (disclosure: Stott sent me a print set to use for this video). However, they are also available electronically, and a complete digital package is $55.60. That is a much more reasonable price, and (in my opinion) well worth it.