Jobs at small San Diego companies nobody posts about - 22 weeks in

A friend who works at a local manufacturer says there are openings not advertised online. I am in San Diego, in case local advice matters. 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.