Industry classification systems are created to promote data comparability. They are often featured in books, databases, and government websites. NAICS (current version) and SIC (older version) are the most widely used in the U.S., although many sources also have their own systems.
An industry association is established to advocate for the industry and associated companies. They collect and provide unique data/articles/reports. Sometimes these sources are on their websites for free.
To find the industry association websites: