Q. Where can I search for Think Tank reports?

The Harvard-Kennedy School provides a Think Tank search engine that "searches the websites of institutions that generate public policy research, analysis, and activity. These sites are affiliated with universities, governments, advocacy groups, foundations, and non-governmental organizations. Inclusion is based upon the relevancy of subject area to HKS coursework and scholarship, the availability of the think tank’s research in full-text on the website, and the think tank’s reputation and influence upon policy making. The list represents a mixture of partisan and non-partisan think tanks."

See https://guides.library.harvard.edu/hks/think_tank_search

JSTOR hosts a growing curated collection of more than 50,000 open research reports from 187 think tanks and research institutes from around the world. These publications are freely accessible to everyone on JSTOR and discoverable as their own content type alongside journals, books, and primary sources.