Selecting the right database can be the best way to find relevant sources. You may want to start with a general database, like JSTOR and then move on to a more specialized one like Artemis Literary Resources. If you can't seem to find anything on your research topic, try different keywords or another database. Remember, you can always ask for help by using the ask a librarian box.
The simplest criterion for distinguishing book reviews from literary criticism is the time of publication of the review/critical article compared to the original publication date of the book. Book reviews are written around the time the book was originally published; literary criticism appears in later years. For example, reviews of F. Scott Fitzgerald's The Great Gatsby that appeared in 1925 or 1926 (right after the novel was published) are book reviews, while literary criticism about the novel continues to be written today. MLA Bibliography is an important index of literary criticism.