You could set each referral up as a "child" of the "Parent" company (referrer). It's not searchable, per se, but you can easily see children of an individual company under "Related Companies" info panel.
You can also set up an active list with the criteria "Parent Company" (under Company properties) "is known" and order by Parent Company to get a quick overview (albeit ont a count) of your referrers.
Let me know if this helps, or if you'd like any further info on any of the above.
Did my post help answer your query? Help the Community by marking it as a solution "The rest of my advice has no basis more reliable than my own meandering experience. I will dispense this experience... now!"