OneSearch! is an excellent tool for finding articles and other publication types in all subject areas, including marketing.
Other tools that specialize in finding articles in marketing and other business areas are listed here.
If a company is small or new, it may have been covered only in a local newspaper or a large company directory.
If the database provides only an abstract (summary), look for a yellow Find It button or the words Find It @UNI; clicking this will open up a window that is supposed to indicate whether the full text is available in another database or in print at the Rod Library building.
Search Google Scholar collection of articles and other academic sources. Covers all subjects, not just business.