Does anyone know if there's a website that keeps track of One Piece tankoubon (or just general manga tankoubon) sales? I know Oricon publishes a weekly manga sales chart, but I haven't been able to find a source that tracks historical sales. I know One Piece is the best selling series, generally averaging 1 million in first week sales and 2 million overall, but it would be great to have more exact figures per volume.
Rationale for my question: I'm a chart/sales data geek and keeping track of sales trends in line with popularity and the economy piques the statistician in me. Thanks!