If a patron is looking for an "authoritative" copy of a treaty for a source hunt, follow the steps below.
If they want more than just the official text of the treaty, walk them through the standard procedure for finding secondary sources. In addition to monographs and journal articles, we have commentaries and compiled legislative histories (most using the term of art "travaux preparatoires") for many of the major treaties in human rights, international organizations, and international criminal law.
Hopefully, the author provided a halfway decipherable citation to the treaty. The good news is that almost all the Bluebook-approved sources (see Rule 21.4.5) are readily available in HeinOnline.
1. For the following official US sources, go to Hein's Treaties and Agreements library and click on "Treaty Publications": UST (U.S. Treaties and Other International Agreements), TIAS (Treaties and Other International Acts Series), STAT (Statutes at Large, for pre-1945 treaties), Senate Treaty Documents, and compilations like Bevans. Hein is running a bit behind on TIAS agreements, so double-check the State Department's site if you suspect it's a very recent treaty.
2. For UNTS (United Nations Treaty Series) or LNTS (League of Nations Treaty Series), go to Hein's United Nations Law Collection and use their extra-user-friendly "Enter a United Nations Treaty Series/League of Nations Treaty Series Citation" links.
3. If the treaty isn't available in one of the above, the author is supposed to supply an ILM (International Legal Materials) citation instead. ILM is an American Society of International Law journal, and is available both in the Treaties & Agreements library and in Hein's regular Law Journal Library.
4. For very old, historical treaties, the preferred source is CTS (Consolidated Treaty Series). This is available in print, and in PDF via the Oxford Historical Treaties database.
5. For organizations other than the U.N., or for bilateral treaties to which the U.S. is not a party, the cite should be to an official IGO publication or a national treaty publication, if available. Use a citation tool to figure out the cite and see if we have it in print, or check the tools for foreign law to see if it's online in PDF somewhere.
If the author didn't supply a citation, or if the cite is indecipherable or wrong, try the following to get a cite, and then use the sources above for the full text:
1. Check Minnesota's handy Frequently-Cited Treaties guide, which provides a fully Bluebook-compatible cite for the heavy-hitter treaties, and also links directly to PDFs in Hein much of the time.
2. ASIL's EISIL treaty database covers far more treaties, and is browsable by subject, although the search function is less than efficient. (I find it better to run a Google search with the site limited to eisil.org.) Also note that the documents EISIL points to in that top link are not necessarily from official sources; they're just the most stable source available on the open web. Most of the time, the version EISIL points to in the link with the treaty's title will not be sufficient for journal source hunt purposes. Instead, click on the "More Information" link, which will take you to a full record with a description, entry into force information, and cites to Bluebook-approved sources like UST and UNTS.
3. If you think it's a current treaty the U.S. is a party to, check Treaties in Force or Kavass's Current Treaty Index. TIF is available in the Hein Treaties and Agreements library under the "Treaty Guides and Indexes" link, but Hein appears to be running one issue behind with TIF. I prefer to go to the State Department instead to download the most recent one, and then do a CTRL-F search for whichever treaty I need the UST/TIAS cite for. Current Treaty Index is up to date on Hein, and it can be used to find newer treaties by KAV number in the "Treaty Publications" under KAV Agreements.
4. For brand-new treaties the U.S. is a party to, or those still somewhere in the pipeline with the Senate or the executive branch, go to the Treaty Affairs site of the State Department.