Hold a party for your best sources of referrals. Make it worth their while to show up by providing great food, drinks and entertainment.
If you show them you appreciate their help, they’ll continue to bring you leads and you’ll all end up better off for the arrangement between you.
Consider giving a yearly gift to those who bring you the most referrals. It doesn’t have to be something big, even a bottle of nice wine will do, but it shows them you care.
For example, real estate agents could get tips from local HR professionals on people moving to the area to start a new job.
Consider who might have an insider’s view on who would be interested in what you’re selling. Who would know of people who would need what you are selling?
When they do, you have their contact information as a new lead, and of course this is a targeted, niche specific contact.