I recently decided I wanted to learn more about the Dehn invariant, so I did what I always do and went on MSE and MO to get recommendations. I found this link, which suggested a book called "Theory of convex bodies" by Bonnesen and Fenchel (ISBN 9780914351023). Unfortunately, the book seems to be out of publication, and I can't find any used copies or electronic versions. Moreover, my local university library doesn't have it in the catalog.
Is there any way for me to see this book? What are strategies for finding old textbooks like this?
PS: Moderators, please make this question community wiki, and/or migrate it to MO if it would be more appropriate there.