So much you'll wonder why you do this. Remember that rejection is never personal, and that one win in a hundred calls could keep you in bacon for years. Do mailings, but not exclusively. Follow-up on them. Contact the State for lists of technology companies.
Some counties maintain decent lists as well.
Yeah, all of this takes a lot of time. That's why I believe in taking on a partner dedicated to sales. No one has enough time to sell and do the work. Know what you do well, and do it. Surround yourself with others who complement your skills.