1) News sources: Most national news publications have annual “What Lawyers Earn” articles. Try the Wall Street Journal, U.S. News & World Report, ABA Journal, and other places. Use a search engine or index to locate these.
2) Professional Associations, e.g.: American Bar Association (ABA) and National Association for Legal Professionals (NALP), Pacific Northwest Paralegal Association
3) Private sources, e.g.: Robert Half Legal “2013 Salary Guide” on compensation in the legal field.