You will find Washington Post book reviews, back to 1877 and through 1998, in the Washington Post Archives database linked here.
NOTE: You may find a reference to a review in something called Book World. That was, in fact, the Washington Post book review supplement's separate title for some years.
You need to follow the example below carefully.
If you want to search for reviews of the book pictured here, published in 2011 (you can find this date easily in Amazon!), you would do the search pictured below.