The Bureau of Industry and Security (BIS) -- formerly the Bureau of Export Administration (BEA) -- regulates U.S. exports, particularly for purposes of national security. The Bureau's Web site posts a lot of information about how to satisfy U.S. export regulations, including selected Advisory Opinions.
The GPO posts the Bureau's regulations.
The Bureau issues Denial Orders that limit or prohibit people from exporting goods. The Orders are published in the Federal Register. The Bureau post a Denied Persons List that tells you where you can find the related Denial Orders in the Federal Register.
The Bureau also posts a number of other Lists to Check, including an "Unverified List," an "Entity List," a "Specially Designated Nationals List" and a "Debarred List" and a list of "Nonproliferation Sanctions."