This is a strange question, but does anyone know of a Catholic store in Madrid? My friend is becoming a NYPD officer and I'd like to get a San Miguel Arcangel medal. Anyone?

There are lots of shops between Sol and Plaza Mayor selling religious objects. Try Calle Postas and Calle Mayor. I can't remember the names or exact addresses right now, but a stroll along these streets should lead your friend to what he's looking for.