I have a very specific group of people that I want to market my services to. I have lots of experience with this group and feel that my background would benefit their organizations. My question is how do I approach them without breaking the rules of contact? My potential clients (thinking positive

) are all over the country and not just down the road at a social networking event. Can I send unsolicited email with an introduction or snail mail postcard / brochure / introduction letter? Another option would be advertising in industry magazines, but I don't feel that is as direct of a shot as just contacting them individually.
Thanks!
Wendy