Pronouncements of states can take the form of Department of state memorandums, letters from legal advisors, U.S. 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.
Direct links to the official government websites, as well as citations to (and links where available) secondary sources and research portals that you may find useful.
Organized in reverse chronological order
Books and Journals that describe U.S. state practice in international law.
Often included are citations to or full text of primary documents.
The American Journal of International Law, currently includes a quarterly segment entitled "Contemporary Practice of the United States relating to International Law."
It first appeared in volume 53, 1959.
According to the Editors note at the time this segment was created, "Criteria for the selection of materials may vary with experience, but the guiding purpose will be to select materials which reveal contemporary practice by the United States in invoking and applying principles, rules and procedures of international law or policies relating thereto."