One of the most direct ways to locate gas providers in a region is to visit a website of the town, county or state in question. Gas companies that operate over a large area sometimes have an online list or map of areas that they serve.
Seattle.gov is one city website that posts information about utility services for the community, including gas services. Seattle gives its residents a couple of options, and links to the providers in question. The website of Fairfax County, Virginia, fairfaxcounty.gov, identifies gas utility providers for the county, and includes customer service and emergency contact information. You can look up the website of your own city or county of residence to see if they provide such information.
Information on gas providers on the state level is sometimes available from the state agency that regulates energy resources for the state. For example, the Georgia Public Service Commission has a list of certified gas marketers for the state of Georgia for the benefit of area residents.
A less direct method you can use is to look at the websites of individual providers to see whether they operate in your area. For example, CenterPoint Energy has a color-coded map showing areas where the company provides natural gas operations.
If you are interested in a provider based on that provider's ranking in a particular field, then you can visit the utility rankings list on the website of the American Gas Association.