The Bureau of Labor Statistics (BLS) website includes a Location Quotient Calculator that enables users to quickly and easily calculate location quotients for any county in the U.S. Annual data from 2001 to 2010 is available allowing users to analyze changes over time. Location quotients can be calculated up to the three-digit NAICS level. However, in many cases, data at the industry sub-sector is not available for counties with smaller populations as the data is suppressed. Regardless, this a valuable and easy-to-use tool.
If you need a good, brief, basic refresher on Location Quotients, try: Use Location Quotients to Identify Local Strengths, Opportunities, and Industry Clusters by Martin Shields.