Jobs at small Sacramento companies nobody posts about after 6 years as a school bus driver

A friend who works at a local manufacturer says there are openings not advertised online. They prefer people who can start within a couple of weeks. 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.

Small employers often hire on recommendation. Ask neighbours, former co-workers and your library.