Data Sources for Proprietary Deal Sourcing

For those working in M&A, PE, corp dev, or acquisition entrepreneurship, what data sources have been most useful for building targeted outbound lists?

We use Grata for company screening and revenue estimates, alongside sources like the BBB directory to identify businesses that might otherwise be missed. However, company data can be outdated, and determining the actual size and fit of a privately held business often requires additional research.

I’m particularly interested in tools that help with three things: identifying relevant companies, verifying company size, and finding direct owner or executive contact information.

Have you found Apollo, industry-specific directories, or other enrichment tools particularly effective? Which sources do you trust, and where do you still rely on manual verification?

Interested in hearing what has worked in practice, especially for smaller, founder-owned businesses.