Yearbook of the United Nations (1946-) & Yearbook Pre-press (2015-2017)
United Nations Legal Publications Global Search supports searching in:
UN legal yearbooks (including Yearbook of the International Law Commission);
Repertoire of Practice of the Security Council;
and Repertory of Practice of United Nations Organs.
HeinOnline's United Nations Law Collection includes many U.N. yearbooks.
Digest of United States Practice in International Law (1989-)
HeinOnline's Foreign and International Law Resources Database and HeinOnline's series: Foreign Relations of the United States
Foreign and International Law Resources Database includes:
Older digests of U.S. practice in international law
Some international law year books
International documents reprinted in International Legal Materials (I.L.M.).
Avalon Project of Yale Law School Lillian Goldman Law Library
Contains historical legal and diplomatic documents. Provides full-text of some documents mentioned in international law digests.