The following title is an annotated bibliography of book review sources. It is useful for finding obscure book reviews, including many in non-English-language sources.
Another approach to finding reviews not otherwise uncovered by the above resources is to enter the phrase books reviews in the Cornell Library's Catalog as a subject search. Browsing the list of subject headings generated by this search reveals many additional sources of book reviews. And remember that the reference staff is available to assist you.