This is not a "put food on the table tomorrow" strategy, but it does work: start blogging how you solve the problems of the people whose problems you want to solve. Continue blogging for a few years, gradually building up a reputation for yourself as a topical expert in the community.
On a related note: get speaking gigs at conferences or support events that your target customers attend. It will take some work to establish yourself as a domain expert, but once done it's likely to bring you a steady stream of prospects.
Good call. Back in the day, my family's business started through direct mail, at first with letters and later with colored flyers. The flyers worked better. We found mailing lists from funding agencies and other public or quasi public sources. This was exceedingly difficult and time consuming, but it worked.
Nowadays, a lot of our clients find us via Google and our blog at http://blog.seliger.com , but that takes more time to build. Still, we try and put a fair number of likely keywords in the titles of posts, which helps. We started ours after the Wall Street Journal ran a story on that issue, and it was like, "Why didn't we think of this earlier?"
You'll have to beat off offers with a stick.