In the past, when I investigated data / backfill data sources, the data presented two problems: it was either costly or the quality was dubious at best.
I once fancied the idea that some of the larger providers might make their "expensive data" available on a revenue sharing basis. When I made inquiries, the conversation never advanced. Too bad, as it appears some are withering for wont of revenue.
What I'm looking for is mostly curated "seed data" in various verticals, free or low cost or rev share.
If it's not as easy as just Googling some companies, and current data providers won't do it, then perhaps the best way to get 'real' data is a local phone book and a telemarketer calling businesses to gather information.
It's also a good time for the telemarketer to upsell the business from their 'free listing' to an enhanced listing.