Use the Reference librarians at OKU:
They can help you not only locate archival collections elsewhere, but also the vast numbers of digitized sources that are already available to you. Don’t expect all of your materials to be available online, but if you are dealing with rare books, newspapers, serials, or other sources, you might be able to find them already digitized.
Talk to Interlibrary Loan
Even if archival collections are not digitized, heavily used or very important collections at most institutions are available on microfilm, which can usually be lent to Cornell patrons via ILL, or have single reels or some sections of reels sent to you on PDF. Olin has great microfilm scanners that can convert microfilm to PDF as well, so that you can save materials as needed. ILL might also request single items from archival collections. It is always worth a try.