The call numbers for customs law are around KF6690 in the Library. Browsing the shelves there may also help you find relevant secondary sources. Further, you can do a subject search in the library catalog. Possible subject headings to use would include:
Customs Law and Administration
Import and Customs Law Handbook
Corporate Counsel's Guide to Importing under the U.S. Customs Laws
International Trade Reporter Decisions
Dictionary of International Trade
To find articles on customs law, use the major legal indexes: Legal Periodicals and Books, LegalTrac, or Index to Foreign Legal Periodicals. Links to these and other databases are available from the library's page on legal periodicals.
There are a number of law journals in the library dealing with international trade. To find them, you can do a keyword search in our catalog for the words "international and trade," limited to the location "Journals".