You will get limited results if you try to search for "primary sources" in library databases since the Library of Congress does not use that subject heading. Try searching these search terms instead:
You will get limited results searching for the word "autobiography" since the Library of Congress does not use that subject heading. Try searching for "biography" but then look to make sure that the author is also listed as a subject. That is your clue that the person is writing about him or herself, and that is a primary source.