Book reviews, especially scholarly or lengthy ones, can be good sources of information about the author of the book, his/her scholarly background and biases, as well as how this book compares to others in the field (or if it's unique).
Use the indexes to the scholarly literature in your field (and related fields) to find book reviews in the scholarly journals for your discipline.
WorldCat is a searchable database of thousands of library catalogs from around the world.
You can search here to see if a book you can't find through OneSearch exists elsewhere.
Good sources of information are well-organized. Searching in article and book databases is easier if you know about how they are organized, so here are some tips to make your search for resources more effective and less frustrating: