The following resources offer financial information for companies.
International directory of company histories
4th Floor Reference--338.7409-INT
Waterlow's unquoted companies
4th Floor Reference--338.740942
The Library has lots of material on specific companies and sectors; use the Enterprise catalogue to locate these items. Search Business Source Complete to find journal articles about specific companies.
Annual reports are good sources of data about companies including financial information. Most companies have their own web sites. There are two major sites, which provide links to companies: