Research & publications from reputable think tanks, NGOs, and policy organisations, can be an important complement to the academic literature (books and journal articles), especially for research topics that have policy dimensions.
The policy literature is generally not included in academic search engines such as the library catalogue, Scopus or Google Scholar. However you can use databases that cross-search the output of these organisations to help save you time. The main ones to try are Overton Policy Documents and/or Policy Commons
