Think tanks are a good source for finding additinal information on your issue. Think tanks produce documents and research that are inteded to influence public policy at the state and federal levels. Most think tanks will identify as non-partisan but they are typically heavily biased toward one political persuasion or another. They are technically, "non-partisan" becasue they are are not affiliation with any policital party. Here is a list of some of the many Think Tanks that exist in the United States.
There are also a great number of Think Tanks that focus on one issue. For example the Kaiser Family Foundation is highly focused on American healthcare policy.