In the reading I have done on this site, it sounds like a band hiring a sub in a pinch is a pretty normal thing. It sounds like a good way to experience different bars and crowds, play with different people, and make a few extra dollars. How do you get yourself on a list of people to call? Does anyone advertise themselves as "available" for that sort of work? Just tell all of your musician friends that you'll help out if they need it? I think I've got the chops and experience to do it, and I'm always up for a challenge. How do you do it?