There are many databases you can use to find book reviews. For older titles, you can search Historical Abstracts, JSTOR, or Periodicals Archive Online. For more recent titles, you can try Historical Abstracts, American Bibliography of Slavic and East European Studies, Project Muse, Expanded Academic ASAP, Academic Search Complete, and Arts & Humanities Citation Index (Web of Science).
It typically takes 1-2 years following publication of a new book for the reviews to appear in scholarly journals. Reviews in the periodical press, such as the Times Literary Supplement or the New York Times Book Review, will appear long before the reviews in scholarly journals. Of all the indexing services, Arts & Humanities Citation Index seems to pick up the scholarly reviews the earliest.
If you are looking for reviews of a book entitled, Mothers in the Fatherland, by Claudia Koonz, published in 1987, JSTOR is a good starting place. From the basic search screen, simply type the following string:
rt: "Mothers in the Fatherland"
where rt stands for "reviewed title," followed by a colon and the title of the book enclosed in quotation marks.
The full text of the review is available by clicking on the citation.
Project Muse offers the full text of approximately 300 journals in the humanities. To search for a review of Professor Todorova's book, Imagining the Balkans, first published in 1997, go to the advanced search screen, type the title in the search box, use the drop-down menu to select "title reviewed," and limit your search to reviews by checking the box at the bottom of the form.
The full text of the reviews is available by clicking on the links provided.
If you are looking for reviews of Yuri Slezkine's book, The Jewish Century, published in 2004, use the Advanced Search option in Historical Abstracts and check the box for "reviews" at the bottom of the search form. You can use the Term Browser to insert the author's name in the search box, or you can put the title of the book in quotation marks in the keyword box.
If you are looking for reviews of Karen Barkey's book, Empire of Difference: The Ottomans in Comparative Perspective, published in 2008, go to the advanced search screen in Expanded Academic ASAP, and type the title of the book in the search box. Use the drop down menu to select "Named Work."
This is a relatively recent book, so there are not a lot of reviews available. It usually takes a year or more from the date a book is released for reviews to appear in scholarly journals. One of the reviews listed here was published in the December 2009 issue of The Journal of World History.