When researching treaties to which the United States is not a party, the same research steps apply as indicated in the U.S. Treaty Research. You will be interested in finding...
Bilateral agreements can be more difficult to locate. Sources to consult include the treaty series, statutory compilation, or official gazette of one of the country parties involved.
If you are unable to locate the treaty series of either country party, consult the WorldLII web directory of treaties and agreements by country.
Country research guides and web searches are another effective way of locating bilateral treaties. The Foreign Law Guide, Library of Congress, and Globalex all have research guides pertaining to the law of individual countries.
Many intergovernmental organizations serving as depositaries to multilateral treaties will make these treaties freely available on their websites. For example, the United Nations Treaty Collection (UNTC) is the treaty compilation of the United Nations and is freely searchable online. Other international organizations that also serve as treaty depositaries include the Council of Europe, the Organization of American States and the Hague Conference on Private International Law.
Another option is to consult an online database of treaties organized by subject matter such as the Human Rights Library produced by the University of Minnesota.