Anyone can be a referral source!  Download this guide of the people you interact with on a daily basis to help you get to your goal of 250 people in your sphere of influence.  Plus, no matter what your real estate focus, there are high-value referrers who network with and have lots of connections within your speciality.  Search them out, introduce yourself, add them to your sphere, and start marketing to them!  If you can make it to 250 people in your sphere of influence you'll have a steady stream of referral income.