Reviews for comparative religion resources are found in many online and print titles. Two general online (see links below) and print indexes are available: Book Review Digest (Z 1219 .C96 Ref) and the Book Review Index (Z 1035 .A1 B6 Ref). Another excellent print title for book reviews in philosophy is the Combined Retrospective Index to Book Reviews in Humanities Journals, 1802-1974 , located in Waldo Library, Central Reference (Z 1035 .A1 C63x).
The following online databases are excellent for locating book reviews. The first two are especially useful for reviews of philosophy and religion books, but these fields are so broadly based that any general humanities or social sciences database may include relevant reviews. See the titles found under the tab labeled Article Databases, e.g., Humanities Abstracts and Humanities and Social Sciences Index Retrospective.