One easy way to find the auditor of a public company is to use Mergent Online. Simply search by company name or ticker symbol. When you view the default "Company Details" screen, the company's auditor and legal counsel will be identified in the blue bar at the top of the page.
It is also possible to use the Advanced Search function in Mergent Online to identify firms that share a particular auditor. If you need any assistance, please contact the business librarian.