Pronouncements of states may, in the U.S., take the form of Department of State memoranda, letters from legal advisors, legal or other briefs, position papers and remarks. Many of these are freely available on the U.S. State Department website. You can also use digests and secondary sources to find commentary on, citations to, or the full-text of pronouncements of the state on international law.
International Law As Law of the United States
by
Jordan J. Paust