There are a number of Libraries databases that might help you to build a list of new and/or early stage businesses. Your very best starting point is probably CBInsights, which allows you to do an Advanced Search for Companies wherein you can specify a large number of metrics, but particularly 'Year Founded'. So you could search for companies, for instance, all founded in the past year. You can do the same thing in a Company Search in the Preqin database, though this database also has a category of filter for 'Company Stage' wherein you could specify that you're interested particularly in 'early stage' companies. If you're looking more for summary statistics regarding new business startups, the Census Bureau has a product called Business Formation Statistics which tracks new business applications data.
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