Personal training?

You need to take an active role in marketing your services, and what you have done up to this point, for the most part is passive.

Here are some ideas.
1. Offer a one time discount, or a charitable donation in your clients name to your existing clients for referrals. This is simple taking passive word of mouth to the next level.
2. Pubic speaking and seminars can be useful. Your chamber of commerce probably has monthly meetings, see if you can talk at one of them. Just do not make it a commercial, but a call to action to get in shape, ideally without your services. The people that want more, can pick up flyers, or cards advertising your business, or even talk to you after the event.
3. What about contacting the local high school coaches to assist with off season training of their atheletes. They may have some leads for you.
4. Do you stay in contact with past clients. People drop out for a number of reasons, they get busy, they get injured, or whatever. Sometimes all it takes is a phone call to get them interested again. If nothing else, maybe they can give you some names of other people that might be interested, even if they are not.
5. What about employee health programs and insurance plans. More and more benefit programs are either sponsoring, or subsidizing gym/training programs. If you get in good with a local business, you could add a number of clients for very little work. This is also an area of potential for public speaking. Again, a free get healthy seminar, with no commerical content is a possibility.