In the OneSearch you can use the Dates facet to set a range of publication dates you want to focus on. If you're looking for 19th century resources, for example, you might save yourself a lot of time if you limit your search by date to exclude results from the 20th century.
Once you've done a search in the OneSearch, you can limit your search results so only materials in Special Collections & Archives are displayed by selecting the "Special Collections & Archives" option within the Location facet group on the left side of the screen.
Sometimes books are added to Special Collections & Archives as collections around a single subject or topic. For example, the Vern and Bonnie Bullough Collection on Sex and Gender contains thousands of titles that focus on human sexuality and gender studies.
If you find a book with a Collection designation, you can click on the linked title to bring up a list of other books that are a part of the same collection. Most or all of them will probably be about the same topic.