If you haven't already, you might consider on a test basis including either a Business Reply Card/envelope or SASE (Self-addressed stamped envelope)or card as part of your mailing. Either on the card or your flyer include an area for the prospective client to fill in their contact information, etc.(keep it simple) This is obviously a more costly way to reach your market but the response for same could well outweigh the extra expense. The important thing is to TEST! TEST! TEST! until you get it right.

By the way, a 3% response is considered about average for direct mail.