Unfortunately, no one source has all of the information from the U.S. Congress digitized. So, you will need to determine the years and congresses you need covered before you select a source.
More recent information is found on Congress.gov. Older materials are found on Newsbank Readex. Congressional (ProQuest) includes much information including index information to find data not in our basic subscription. Heinonline's databases and libraries often bridge the information gap. Google Books also has older material, but the danger in using it is that it makes no attempt to be comprehensive.
If you have the CIS number found in Congressional (ProQuest) or in the Law Library's print collection, it may be possible to find the document you need in the Law Library's microfiche collection of the U.S. Congressional Serial Set.
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The United States Congressional Serial Set, commonly referred to as the Serial Set, began publication with the 15th Congress, 1st Session (1817). Documents before 1817 may be found in the American State Papers. (Both are available on Newsbank Readex.)
The Serial Set contains the House and Senate Documents and the House and Senate Reports. The reports are usually from congressional committees dealing with proposed legislation and issues under investigation. The documents include all other papers ordered printed by the House or Senate. Documents cover a wide variety of topics and may include reports of executive departments and independent organizations, reports of special investigations made for Congress, and annual reports of non-governmental organizations. During the late nineteenth and early twentieth centuries, executive-branch materials were also published in the Serial Set.
The serial number is a unique number applied to each book in the series of congressional publications running consecutively from the 15th Congress. The serial number may be useful for locating items, but not for citation. The documents and reports series have three numbers:
Documents and reports can be located using the volume or serial number but should be cited using the publication number and Congress and session number.