The best database for finding major national or international competitors is IBISWorld.
The best database for finding local competitors is AtoZacademics. Start with the first box, "Find a Business". Click on Advanced Search. The most useful combination is Industry Type and Geography. Use the NAICS code if you know it from your industry research, or use keywords. Define the geography that is appropriate for your market. You can download any results into excel spreadsheets and create maps. will give you a family tree link to assemble a whole company, and it gives size estimates for individual locations (sales, square feet, number of employees) which can give you a reasonableness check on what performance levels are possible.
The other place to find breakdowns of numbers of enterprises by state or country is Business Source Complete.
If you can identify a smaller or privately held company in the same industry, you can look them up in Hoovers, which contains brief profiles of many companies and each report contains a list of competitors,
