Advocacy Groups, Interest Groups-a collection of individuals who seek joint ends through political action and tend to have narrow goals focused around an issue or issue area. These can be: private groups, sponsored by corporations, private industry; non-profit or citizens groups, e.g., AARP, Children's Defense Fund; labor groups. The organizations may conduct research or use others research to support position, provide policy briefings, etc.
The legislative section or "news alerts" area of the websites of advocacy groups can be useful sources for bills that are directly related to their mission.
How do I find advocacy groups?
You can try thinking more generally about trade or professional organizations that may be invested in a particular topic or bill, e.g., National Education Association, Children's Defense Fund, National Immigration Forum, American Academy of Pediatricians, etc.
Use Google to find advocacy organizations: Try searching your topic or legislation, limiting the search to site:org. For example, immigration site:org; no child left behind site:org. Or you can use phrases such as legislative action children, immigration advocacy groups, etc.