Law of Reciprocity
You must first give to get. Giving creates a debt; an imbalance. The debt is paid by returning the favor.
A new patient referral can be gift or a get.
If you want more referrals, give more referrals. When appropriate, refer to the MD down the street or the pediatrician who "gets it." Refer patients to a good plumber, roofer or restaurant. Assume the role of a concierge, solving more problems than just their admitting complaint. Become the "go to" person for anything and anyone and watch your influence (and reciprocal referrals) grow.
The Law of Reciprocity takes time. The error that many make is they superimpose their own sense of time when invoking the Law. Trust it will come back to you, next month, next year or some time in eternity. But it always comes back. What you give away (good or bad) always returns.