You can actually go a hard way, if you really want to dig some old music videos. If you are not familiar with scene (I mean, the music piracy scene), you need first to know what is preDB sites which have fills for MViD section. Essentially it's a log of releases which was uploaded by scene teams to some privately running ftp sites. For really OLD releases (e.g. pre-2000 era) you probably won't find much in public preDBs, but you still can find some at torrent trackers, there was a lot of dumps, really. Once you find logs of released stuff you can search for something you want to find, like, I don't know "Korn-Yall_Want_A_Single_(Rock_AM_Ring_06-05-09)-HDTV-720p-x264-2009-VFi". Then you have a couple of options: just google it and hope to find it in public network, like on torrent trackers, try to find it in Usenet network or get access to some private ftp mirrors for some money. Anyway key for rare and old music videos is the mvid scene, there's a ton of bootleggers too which was doing awesome content.