Statistical compendia provide a variety of statistics from a variety of sources. Even if the data that you want are not there, look at the footnotes or source notes for relevant tables for pointers to more comprehensive sources, often having more detailed or comprehensive statistics.
Look for compendia under the "By Topic" tab above.
Strategy 1. Start with a finding aid. Details
Strategy 2. Start with a statistical compendium.
Strategy 3. Start with an agency or organization. Details
Strategy 4. Look for relevant statistics reported in books or journal or newspaper articles. Find the source of those statistics.
Strategy 5. Search the Internet using your favorite search engine.