In the example below, we have done a simple search in USearch using the title of the book, Frankenstein. From the Tweak my results left sidebar on the results page, you can click on "Show More" under Material Types to find the option to limit your search to just reviews. Click on Reviews, and this will refresh your list of search results to show just reviews.
To narrow down your results even further, you can select Book Reviews under the Topic refine option on the results page.
Your results list should now only show reviews.
USearch is a good place to start if you don't have detailed bibliographic information about the book you are reviewing, or if you aren't sure which index or database to use. It will search through many different databases and review sources at the same time.
A quick search using the title of your book limited to Reviews as Material Type will give you many results.