Gene - here are a couple of thoughts, fwiw.
1.) Email is cheap, practically free and doesn't have to be spam. You could set up an opt-in email with a regular short informational blurb showing some of your findings that have benefited clients. When I was first in the business an inspector found an attic furnace that had been red-tagged by the city for a safety/design flaw. The owner had no idea he and his family had been living in danger of a catastrophic fire.
2.) Craigslist comes to mind, although the rules have changed so you might have to get creative. Set up a one page web site describing your service and direct inquiries there. Maybe show dramatic pics of hidden damage, water damage from leaking pipes, dry rot, etc.
3.) In addition to what Jonna said, in a previous life, I would do what was referred to as "courtesy calls". Develop a route for all the brokerage firms in your patch and stop by to introduce yourself, drop off a card or flyer, or bring doughnuts.
4.) Facebook and Linked-in might be other resources.
Just a few thoughts before my second cup o' coffee.