Critical analysis essays are available right here on eNotes for both of these novels.
For Tender is the Night, the “Essays and Criticism” material is probably the best in terms of critical literary analysis. The first essay presented provides an analysis of passages of dialogue and “suggests that Dick Diver’s tragedy is internal and not caused by the corrupting influence of Nicole’s wealth.” The essay offers a valuable analysis of the novel and its core meaning(s).
The body of critical analysis material on The Great Gatsby at eNotes is even more comprehensive. Numerous essays treat the novel with a detailed, text-based approach. If you are interested in tying the novels together as modernist works (dealing with Freud’s influence on modernism and/or the morality of materialism), you may be interested in reading the essay, “A Modernist Masterwork.”
If you are looking for critical analysis elsewhere (which may take more time to track down, purchase, etc. but is certainly worthwhile if you have the time/opportunity) there are many good pieces of criticism on Fitzgerald’s work. Personally, I enjoy Alfred Kazin’s writing on Fitzgerald. (An American Confession and F. Scott Fitzgerald: The Man and His Work may be two items to look up.)
Currently, you can access a critical review of Tender is the Night by eminent literary critic Malcolm Cowley at the New Republic (online). The essay was originally published in 1934 and offers a nice insight into some ways the novel was viewed upon its release.