Visit Census.gov's list of international statistical agencies for a list of official statistical offices by country.
The following sources provide background information on countries around the world, and will include data and statistics that can provide you with the quantitative evidence you may find beneficial for your policy brief.
For further resources to help you locate data and statistics relevant to American foreign policy, please visit the Political Science Research Guide or visit the OFFstats, which allows you to browse free web resources for data and statistics where you can search by region, country, subject area, or a combination thereof.