Currently, the book can be bought at Amazon.com, BarnesandNoble.com and other online book retailers.
http://www.amazon.com/s/ref=nb_ss_gw/104-1182061-8067124?url=search-alias=aps&field-keywords=pen+and+paper+diet

The Pen and Paper Diet: Metric Edition 
ISBN 978-1-4357-1904-0

  The Pen and Paper Diet: Expanded Metric Edition
ISBN 978-1-4357-1913-2

The Pen and Paper Diet: US English Edition 
 ISBN 978-1-4357-1812-8

The Pen and Paper Diet: Expanded US English Edition
ISBN 978-1-4357-1813-5

La Dieta de la Pluma y el Papel: Edicion en Espanol de EE.UU.
(US Spanish Edition) 
 ISBN 978-1-4357-1938-5

The Pen and Paper Diet: Expanded US Spanish Edition