There are more websites and resources available. Checking the online catalog will be helpful. Here are a couple of useful sources-
Treaties and Other International Acts Series (TIAS) This is a series of consecutively numbered, individually paginated phamphlets containg the text of treaties. TIAS is the first offical U.S. Publication. of treaties and international acts. These appear in slip form. Many are also available online via Hathi Trust [NOTE: Treaties must be ratified before they are given a number. Delays in publication could be as long as 5 years!]
United States treaties and other international agreements (UST) Began in 1950, bound form of TIAS This is also VERY slow in being published. Takes several years.
U.S. Senate Treaty Documents (Text of treaties transmitted to the Senate for its advice and consent are listed under this link on FDsys for each congress back to 1985) This is a good source to check when TIAS volumes are not yet published.
Treaty series / League of Nations (This set covering the period 1920 through 1945 is similar to UNTS in that it contains treaties of the League's members registered with the League's Secretariat. Each volume has its own index. Cumulative indexes covering 3 or more years each are also provided.)
Treaties and Other International Acts of the United States 1776-1883[Miller] This source was updated by Bevans (Below)
Treaties and other international acts of the United States of America 1776-1949[Bevans] (Considered the definitive collection of U.S. treaties before 1950. Volumes 1-4 are multilateral treaties arranged chronologically; volumes 5-12 are bilateral treaties arranged by country; volume 13 is the index to the set.
Indian affairs. Laws and treaties (Historic collection covers 1904-1941)
Proquest Congressional Collection contains abstracts and indexing for U.S. treaty documents since 1970