Note on annual reports: These are often annual reports prepared to present to Congress and are therefore frequently published in House or Senate documents. To search these, try ProQuest Congressional (for students and faculty) or Congress.gov (a free website maintained by the Library of Congress).
Note on Westlaw and Lexis: Both of these databases have various federal agency materials and exact content and coverage will depend on the documents.
The most efficient way to find treaties to which the U.S. is a party is to use the U.S. Treaties and Agreements Library from HeinOnline This direct link will bring you to a full treaty index where you can search by keyword, country, treaty name, etc. For a full resource guide on finding and researching treaties and related materials, see the Public International Law research guide. The information applies to treaties covering all areas of law.
To find the primary sources of maritime in other foreign states will depend on the particular state you are looking for. There may be books or journal articles that can also give you background information on a particular state. For example, you can search the library catalog for maritime and the state name. This could give you books like Admiralty Jurisdiction: Law and Practice in Australia and New Zealand. Another example is a resource on Westlaw titled International Trade and Maritime Law in China.
Please see a reference librarian if you need further assistance and know that there are many helpful resources online.