Some fellow forum members have, at times, introduced guys that had no escort profiles. I played with 'Justin' when he was an unknown personal trainer, years before he became Justinherrring on RM
(JustinHerringg - Male Escort - New York City, NY | Rent.Men)
Someone else recommended 'Jewish Boy' on the uppereastside. The kid was super nervous and insisted on meeting in Central Park first. He ended up being real fun. Still does not have an escort profile online.
I will say that these introductions are rare.
Not aware of any agencies anymore. I remember that 'Dave' (forgot the name of his agency) was very good. Sadly, he went out of business.