Build curated lists of small businesses in the US. I mean really quality spreadsheets, with city, state, address, owner name, contact name, email, phone, etc. Do this for business categories, like: bakeries, caterers, dentists, doctors, plumbers, etc. For the doctors and such, I would focus on small town entities who are not part of a large medical practice.

Then you sell exclusive, limited access to the list. The internet is virtually littered with small SaaS applications which are targeted toward small businesses. They are selling software for bookkeeping, time tracking, shift planning, appointment reminders, practice management, etc. These SaaS products have LTV numbers such that direct calling is worth their time.