Jobs at small Omaha companies nobody posts about - any advice?

Two small Omaha employers told me they are hiring but have not posted yet. I worked as a graphic designer before this. 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.

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