When you can't find published primary sources, you may be able to get ahold of electronic or microfilm copies
Much archival primary source material has been filmed over the years, but using it will take some getting used to. Ask for help with microfilm, microfiche, or microcards at a reference desk!
A sense of what it is and how you use it: Using Microfilm
Housed on the lowest level of Kroch Library, the Division of Rare and Manuscript Collections is open for research Monday-Friday and some Saturdays during the semester. Please consult their web site for specific hours. This is Cornell's largest collection of archival and rare book materials. While books are listed in the library catalog, archival collections are described on the collection (rather than at the item) level. Notable collections are described here.
Please note the following policy: before using the collections, you must set up a research account and present photo identification. Set up your account online first--you can request materials in advance of your visit--then when you visit the Reference Room (level 2B Kroch), present photo identification. Be sure to check their web site for specific hours of operation.
You may also be interested in the Kheel Center for Labor-Management Documentation & Archives and its archival collections.