I am having difficulty finding any materials comparing H. D. (Hilda Doolittle) and Ezra Pound. Are there any sources that can help me understand their poetry and compare it?
Both Ezra Pound and H. D. were American poets writing in the early and middle parts of the twentieth century who were personally acquainted. They both lived in Britain and European for extended periods. They were both members of the "Imagist" movement (1912 to 1917). They shared in common an interest in translation, with H. D. focused mainly on classical Greek literature, albeit also with some interest in Japanese poetry, and Pound on a wider range of literary traditions.
Pound was to a great degree the spokesperson of the Imagist movement, writing manifestos, serving as the foreign editor of Poetry magazine, and editing the first Imagist anthology, Des Imagistes (1914). Both Pound and H. D. also participating in a subsequent annual series of anthologies, Some Imagist Poets, edited by Amy Lowell.
A substantial amount of scholarship does exist discussing both of these poets. One widely available textbook you might find useful is Modernism: A Short Introduction David Ayers, the first chapter of which is focused on Pound and H.D.
Your next step should be binary searches on The MLA International Bibliography, the authoritative database for literary scholarship. This database is available through most university library websites; if you have difficulty locating it on your university websites, your reference librarian can help you. When you access the database, you need to do what are known as "boolean" searches, looking for multiple search terms connected by "AND", so you can find works covering both poets. Also, searches on the Imagist movement will access information relevant to both of them. Much of the scholarship comparing the two focuses on the issue of gender. Another important distinction in their later work is that Pound's focus is more cultural and H.D.'s more psychological.