From your friends and family's phones, where they have a contact card for you, nicely labeled.

There's a lot of data flowing around out there, and people overwhelmingly willingly hand it over. You'd think that there would be a law that, having collected that data, they would be required to hold it in confidence - Not for you, but as an agent of the friend who gave them that data. And there likely is, but good luck getting it enforced.