Westlaw: U.S. Treaties and Other International Agreements (contains Treaties and Other International Acts Series (1984-) + United States Treaties and Other International Agreements + United States Statutes at Large (vol. 8-), not PDF)
Lexis+: U.S. Treaties on LEXIS (contains U.S.T. + T.I.A.S. (1985-), not PDF)
The Bluebook: A Uniform System of Citation (Columbia Law Review Ass'n et al. eds., 19th ed. 2010) has a hierarchy of preferred treaty sources:
1) United States Treaties and Other International Agreements (U.S.T.)
The holdings of BLS Library reveal that the last volume of United States Treaties and Other International Agreements was vol. 35, part 6 (1983-1984). This U.S.T. volume includes treaties and other international agreements signed between 1980-1984. Additionally, the web page "Finding Agreements" (provided by U.S. Department of State's Office of Treaty Affairs) provides a date range of 1950-1982 for United States Treaties and Other International Agreements. Thus, the best U.S.-published treaty source is often a Treaties and Other International Acts Series (T.I.A.S.) version. Beginning in 2006, T.I.A.S. became an electronic publication.
2) Treaties and Other International Acts Series (T.I.A.S.), 1945-; or prior Treaty Series (T.S.), 1795-1945; or prior Executive Agreement Series (E.A.S.), 1928-1945
3) United Nations Treaty Series (U.N.T.S.), 1946-
4) Senate Treaty Documents (S. Treaty Doc.), 1981- or prior Senate Executive Documents (S. Exec. Doc.)
5) U.S. Department of State Dispatch (Dep't St. Dispatch) or prior U.S. Department of State Bulletin (Dep't St. Bull.)
Regarding U.S. "advice and consent" treaties prior to 1950, The Bluebook's preferred U.S.-published source is: United States Statutes at Large (Stat.).
In the left frame of this web page, there are links to websites that provide treaties from U.S.T., T.I.A.S., and Stat.