In each individual set list I note whether or not a tape (CDR or DAT or cassette) exists. I receive many questions on this. This is my indication that a recording, usually illicitly made by a member of the audience, is in circulation amongst Neil Young collectors. The quality of these recordings varies. Most are far below that of commercial releases, but some can be quite listenable. These tapes are generally not for sale, but are swapped amongst collectors. I do not necessarily have copies of these tapes, nor can I be used as a source for obtaining them.
The best place to find other collectors would be on the Rust List. There are many wonderful Neil Young fans there, and with a little patience and politeness you should be able find someone willing to share recordings with you even if you have nothing to offer in return. I highly recommend you not go to ebay to purchase bootleg recordings. You will find better quality, more complete recordings available through Rust for only the cost of the media. It might be useful to check the various bit torrent sites out there such as www.dimeadozen.org.
If you have any additions, corrections or comments please feel free to contact me.