Case studies may be found in journal articles. Try the following business databases. Use "case study" or "case studies" as one of search keywords.
This link opens in a new windowBusiness Source Premier provides full text for nearly 8,350 scholarly business journals and other sources, including full text for more than 1,100 scholarly business publications. Coverage includes virtually all subject areas related to business. This database provides full text (PDF) for more than 350 of the top scholarly journals dating as far back as 1922. This database also includes Country Monitor, Industry Yearbook Reports, country reports from the Economist Intelligence Unit (EIU), Wall Street Words, and detailed company & industry profiles from Datamonitor. This database is updated on a daily basis via EBSCOhost.
The following links can help in analyzing or writing a case study.
The following are online case study collections, some are free whereas some charge a small fee.