Many company's will list their mission statement on their web site. Companies will often list their mission in the "About Us" or "Investor's Relations" sections of their web sites.
You can also try Google searches to limit your terms to the company's web site. For example, you could type mission statement site:starbucks.com to retrieve Starbuck's mission statement.
Please be aware that some companies might not have a mission statement. You can also try the above Google search with terms such as "values" or "vision". In addition, in the absence of a mission statement you can also search for an interview with the current CEO since they often articulate the company's values in these interviews.
If you wish to locate an example of an especially good mission statement, you can consult Fortune's List of the World's Most Admired Companies. After locating some suitable candidates, you do try the previously mentioned Google search to locate their mission statements or vision.
This is a good database for articles. Some of the articles will discuss your company's values, mission and philosophy. However, search results will not be consistent since more information is available for iconic companies such as Apple or Starbucks than for other corporations.
Example: I am looking for articles about Southwest Airline's mission, values and culture.
Example: I want to locate interviews with Timothy Cook,the CEO of Apple.
Example: I want articles on leadership at Apple.