State and federal government agencies are a great place to find quantitative data on your topic. Here are a few general websites, as well as some topic specific sites to try.
General Government Stats Sites
Specific Topics
Criminal Justice
Healthcare and Mental Health
Children & Families
Food and Nutrition
Poverty and Homelessness
Other
Each database is going to have a different focus and strength. To be succesful, you are going to have to try more than one of these.