Nonprofits often do research on behalf of government.
Think tanks, NGOs, and social policy research orgs are examples of nonprofits that work on government policy issues.
They produce a lot of valuable and freely available research in the form of grey lit publications that they WANT researchers to find and use.
One of the fastest ways I’ve found to narrow down which nonprofits are working on what, and producing publications on specific issues, is to search in the Candid Catalog of Nonprofit Literature. It’s free, you can search by subject, and it will pull up nonprofit produced publications. From there you can go directly to an organization’s website, to dig deeper.
Candid was created when The Foundation Center and Guidestar joined forces to combine their resources on philanthropy and nonprofit information