The best way to find reviews of philosophy books is to enter the book's title as a keyword search in the Philosopher's Index or PhilPapers. The former allows you to limit your results to book reviews post-search (look under "document type"). Try the same thing in a broader databases, such as Web of Science or JSTOR, if you're looking for reviews in non-philosophy journals.

Notre Dame Philosophical Reviews is an open access journal edited at the University of Notre Dame that publishes a large number of reviews.

New Books in Philosophy is a series of author interviews about recent books hosted by Carrie Figdor and Robert Talisse.

Book reviews can also be found in the following dedicated indexes:

Book Review Digest Plus (EBSCO)
Indexes reviews of fiction and nonfiction English-language books. Reviews are selected from academic journals and library review journals. Includes selected full text. Coverage goes back to the early 1980s.

Book Review Digest Retrospective, 1903-1982 (EBSCO)
Indexes reviews of fiction and nonfiction English-language books. Reviews are selected from academic journals, magazines, and library review journals. Covers reviews published between 1903 and 1982.

Book Review Index Plus (Gale)
Indexes reviews of fiction and nonfiction English-language books. Reviews are selected from academic journals, magazines, and library review journals. Includes selected full text. Coverage goes back to the early 1960s.