One way to find major companies in an industry is to identify one company and identify their main Competitors. (This page is linked from another library guide to Company Information).
With the following databases, you can use the NAICS Code to create a list of competitors in an industry. Some allow you to narrow that list by other criteria, such as geography, sales, private/public ownership, etc.
Most of the sources located ni the Industry Overviews box contain industry statistics. Additional sources: