Official Papers collection is on Law Bod's Floor 0. It holds, for example,
BISD or GATT's Basic Instruments and Selected Documents (for law up to 1995) is at O.GATT per.5
Subject searches to try to SOLO:
World Trade Organization -- Rules and practice
Dispute resolution (Law)
Foreign trade regulation
Arbitration (International law)
General Agreement on Tariffs and Trade (1947 October 30)
Tariff -- Law and legislation
Foreign trade regulation