Databases for Blue Collar Businesses

Hi everyone,

I am working on a new tool to be able to research & contact business owners directly for off-market deal sourcing.

Has anyone come across any interesting databases for businesses in the "trades"? White collar jobs have tons of information on the internet, but curious to see how people have researched HVAC, plumbing businesses, etc. in the past besides old school things like Yellow pages.

Best,
Andrew