The book called "Mom Test" by Rob Fitzpatrick has a section on this. He likes to organize Meetups targeting the types of people you want to meet. But maybe those people don't have time. So also he says there's almost certainly there's a chance you know someone, who knows someone etc. So know what you want to ask, and just put it out into the world on your network e.g. LinkedIn, Facebook etc. "I interested in finding out about x, does anyone know someone in Y/someone who works at Z" etc.