Everyone you mentioned is in the medical or personal healthcare profession. The first step is to try and setup a meeting with each type of client you would like. In this case that would mean meeting with a dentist, counselor, chiropractor, massage therapist. See if you can meet with them for at least 20 minutes or so. Ask them their onboarding process for new patients, difficulties in their business, how they market to get customers and anything you can think of study them. You mentioned you have existing client, interview them and get testimonials on how you solved their business problem. Once you fully understand the needs to each business market your service as a solution to those specific needs and use the wording you learned from your interviews.

Think about it, your client is really your client’s client even speaking with potential patients and asking them what their likes and dislikes are about going to a dentist, counselor, chiropractor, or massage therapist can help in marketing to healthcare professionals. Personal contact definitely works when it comes to marketing, send a personal letter to the healthcare professional introduce yourself, follow up with a phone call and point them to your website. If you performed your interviews well and tailored a landing page to that market.