I need to find information on this person please help.?

I need to find out the last name and the cell phone of a person named ryan for my dad. His wifes name is Sarah and the reason for this is because my stepmom is cheating on my dad with ryan and my dad wants to warn sarah she is being cheated on. i have the guys phone number but i need the girls or a house phone. white pages wont work and i need something free. please help.