Business data can be bought from many private data providers. Free business data is harder to come by but here are some resources, some free and some available to universities and colleges with subscriptions:

Data.Gov

Check out the Finance link – specifically for geographic data, but most of it is not free.

Reference USA*

A database of 14 million U.S. businesses containing verified data, updated monthly. Search by business name and type, executive title, sales volume, year established and more. “HealthCare” provides detailed information about physicians and dentists.  Note that you can geocode the businesses/health care providers using the address field, or you can download the “detailed” version of the data and use the Latitutude/Longitude coordinates provided. Note that you will likely get a more accurately located point if you digitized against a local street centerline or parcel GIS layer if one is available.

* Important: Your University Library must have a subscription to this data base to use it.  Tufts Library has a subscription: Go to the Tufts Library Database Finder and type in “Reference USA”.

US Census Bureau – Business and Industry Data

See also the various State Data Centers that process and distribute census population and economic data as well as other business/finance data – the Census Bureau as a list of these State Data Centers or you can do a web search for “state data center” and the name of the state in which you are interested.

USA.gov – Business Data and Statistics

Not GIS specific, but links to many data portals

Important! Always check with the library reference librarians for other data sources – they have a wealth of experience in helping you find data, and business data can usually be geocoded by address, zip code, or county name.