If you're interested in a specific book, I can try to help you find a legitimate way to access it, such as:
Similar to Line of Action, this is a free web-based tool that provides random pose references to help artists master "super natural" flow and weight distribution. 3. Open Community Resources super natural pose book download free
If you are looking for the specific books (which are famous for their "natural" weight distribution and realistic anime-style anatomy), they are widely available here: If you're interested in a specific book, I