MetaLib and USA.gov are two ways to search a variety of US Government sources with lots of information on social policies at the federal level, the Think Tank Search from Harvard is another useful search engine.
Grey literature sounds a bit unappealing, but it just means literature that isn't formally published -- many governmental and non profit reports fall into this category. One way to search it is to do a Google advanced search restricting to sites that have .org or .gov. For example: