Reply to Songs that haven't been or aren't released

Hey guys I was just wondering when you come across a song that you want to put in your mix on youtube or something and it hasn't been released by anyone on beatport or itunes what is your method of obtaining it? I really prefer buying it from somewhere so that the album art and information comes up correct but half of the songs I'm wanting to put in my mix for a party coming up aren't released they're only on youtube. Thanks guys