Online research into tech meet ups and communities
Using the various amount of websites that provide a place for 3d Printing tech advocates to meet each other whether it be online or on location you could potentially use this as a base for contacting the hosts of each event. Sites like Meetup.com offer a long list of people interested in 3D printing and display the name of the person/persons organizing the event. Once contacted you could release an incentive to get them to initiate the promotion within their groups ie. donate a machine for every 25-50 users who sign up for early bird access. Not only would this reach a large amount of potential clients but this could serve as an opportunity for continued advertising. The goal would be to convince a small group of like-minded individuals to tell hundreds of others without having to contact them all yourself.