This site offers an explanation of Porter's Five Forces, which is a model to describe the profitability of an industry. To access Porter's Five Forces for specific industries, use the MarketLine database, below.
You can find Five Forces Analyses in MarketLine. They are only found in the industry reports. Choose the "Find Information" tab across the top of the page then choose your industry from the list. Click on "Industry Profiles" on the left-hand side of the screen and click on the profile you would like to download (as a PDF). The Five Forces Analysis will be in the complete PDF industry report.