Jobs at small San Diego companies nobody posts about after 10 years as a payroll clerk

Two small San Diego employers told me they are hiring but have not posted yet. One is a print shop, one is an accounting firm and one is a clinic. What do you write in a cold email?

A short email with two sentences about what you can do and your résumé attached worked for me. I followed up after a week.

Visiting in person worked for a trades job. For office jobs, email was better.