YOU, a NON-postal worker, can't put anything in anybody's mailbox legally. Only a postal worker can put mail/flyers/announcements, straw, a piece of coconut pie

... anything into a person's or business' mailbox legally.
Direct mail is legal because a postal worker delivers the advertisement to the people/companies. Make sense?
1. Since you are serving a local audience, check with your neighborhood Wal-Mart store. I see people putting flyers on car windows all the time at mine. Don't know if they have permission, but you can ask.
2. Speak at your local Chamber of Commerece breakfast or dinner. You don't have to join to be a guest speaker. You could give lots and lots of tips during your speech on "Why Does It DO That? Solving the Most Common Computer Problems."
3. Approach a local radio station about being a regular guest to answer the computer questions of listeners who call in. You do the show for free provided you get lots of mentions during the show and lots of advertising leading up to each weekly/monthly appearance.
Just a couple of ideas. Take what you will...
Karon