As to a free database, some recommendations I can offer as being a business librarian for over 20 years I have been asked this question quite often.
1. I would first check to see if your local public library has a subscription to a database such as "Reference USA". This free database allows you to search by NAICS/SIC and you can conduct an advanced search to find business listings in your area. Often this database can be used at home.
More info on this database can be reviewed here:
I would also see if the public library has access to "Ward's Business Directory of U.S. Private and Public Companies"
2. "Manta.com" is another database that allows you to search via SIC:
3. A new service that offers a wealth of information:
Many databases also allow a free 7 day trial so worth trying out sites such as "Hoovers.com" to use for a week and then gather the information you need or decide to subscribe.
I hope the information provided is found helpful as please let me know of any additional questions/concerns you might have. Also if you could please take a moment to rate my assistance so that I can receive credit for helping you today.