As with all legal research, you might be able to jump start your research by looking for secondary sources that will set forth the history of the treaty negotiation and adoption and ideally will cite the negotiating materials. For some treaties, books, articles or IGO websites and databases may provide an article-by-article guide to the history and/or application of the treaty, with expert or scholarly analysis on that article and citations to the relevant travaux préparatoires and perhaps to subsequent jurisprudence/case law applying the treaty. Collections of some or all of the travaux préparatoires have been published for some treaties (see examples in the next box).
To search library catalogs and article finders for books and articles, do keyword searches using some combination of (1) the treaty title or words from the treaty title, (2) words from the treaty subject and (3) words such as travaux préparatoires, commentary, guide, documents, documentary, history, negotiation, analysis, and final record. You should also do a subject search for the name of the treaty.
If you do not find a commentary on your treaty or a collection of or guide to the travaux préparatoires, you can try searching for relevant materials yourself. For example, if a convention was negotiated by a conference of nations under the auspices of the United Nations, then look at summaries of UN codification efforts, such as the Analytical Guide to the Work of the International Law Commission. You can also search pleadings and judgments in international law cases to see whether and how attorneys and courts have relied upon the travaux préparatoires from the treaty (or subject area) that you are researching. Kuehl and O'Brien, International Legal Research in a Global Community 58 (2018). Ultimately, your research may require that you do searches directly in the universe of the documents of the U.N. or other organization that sponsored the treaty negotiation or is concerned with the subject matter of the treaty. See International Organizations.
For national materials on the drafting, negotiation and domestic ratification/adoption of a treaty, you will need to search sources for that country, e.g., U.S. Senate Treaty documents or other congressional publications; national yearbooks of international law and other sources of state practice. An example is Reams and Schultz, The North American Free Trade Agreement (NAFTA): Documents and Materials Including a Legislative History of the North American Free Trade Agreement Implementation Act: Public Law 103-182 (Oceana,2003), available in HeinOnline. See also Foreign Law by Jurisdiction and U.S. ratification & implementation of treaties; Presidential statements, proclamations, etc.
UPDATE: À la Recherche des Travaux Préparatoires: An Approach to Researching the Drafting History of International Agreements, Globalex, by Jonathan Pratter, lists sources for selected treaties, as well as methodology for looking for travaux préparatoires.
See also specific subject tabs, e.g. Human Rights.
The next box lists examples of commentaries and collected travaux préparatoires.
This list is not exhaustive. See the preceding box for advice on searching for additional commentaries.
The Oxford Public International Law database (Browse>Book titles) has a number of the OUP commentaries, for example: