US Customs Directives / Handbooks
https://www.cbp.gov/trade/rulings/directives-handbooks

US Customs Informed Compliance Manuals – Specific by Product  / Industry / Regulations
https://www.cbp.gov/trade/rulings/informed-compliance-publications

Anti-Dumping Scope Search By County
http://web.ita.doc.gov/ia/CaseM.nsf/136bb350f9b3efba852570d9004ce782!OpenView&Start=28.2&Count=30&CollapseView

US Customs Regulations
https://www.law.cornell.edu/cfr/text/19/chapter-I

Harmonized Tariff Schedule
https://hts.usitc.gov/current

China Tariffs
https://hts.usitc.gov/view/China%20Tariffs?release=2020HTSARev16

Tariff Rulings
https://rulings.cbp.gov/home