Marketing & Advertising mentor Jay Conrad Levinson responds:
Satisfy those clients to the best of your ability, and ask them for the names of potential clients as referrals. Your best source of new clients will always be old clients. Get testimonials from them to use in direct mail and online marketing campaigns. The healthiest way to grow is through your current clients.

Since you are able to function with only a couple of clients, I assume that you can engage in one-on-one marketing. Offer free consultations. Write personal letters and follow up by telephone. Grow your business by offering to do pilot projects for prospects, because such projects imply no long-term commitment. By identifying the most promising of your prospects -- probably those closely resembling your current clients -- you can engage in a lot of up-close-and-personal marketing. Once you've identified good prospects, never overlook the power of consistent follow-up.