The Harvard Kennedy School keeps a list of US and Non-US Think Tanks and provides a custom Google search across them all. This is a great place to go to find Think Tank content.
Before getting started with policy research, it is a good idea to start with some background and context to the issues you are investigating. The sources below will help you get to that information quickly.
Use our main library search interface Primo to locate books and other materials in Reynolds Library. When you search from the ZSR Library homepage, you will be taken to a search screen where books are in the center box on the top row. You can see all books from the search by clicking the total number of results in the top of the box, or the More Books link at the bottom. To find books on US Policy Issues, search on the policy and "United States":
Primary Political Science Databases
Other Policy-Related Databases
These databases (listed in the order of likelihood they will be useful to you) will get you to news and scholarly journal articles on public policies from databases for disciplines outside of Political Science. Be sure to include 'United States' as a search term if investigating domestic policy as many of them are international in scope.