There are many "trade friendly" musicians who permit non-commerical (not-for-profit) copying and trading of some of their material. Generally, it's recordings of their live shows that they allow to be traded - i.e. not their commerical releases.
For more information on what it means to be "trade friendly" see....
http://wiki.etree.org/index.php?page=TradeFriendly
Here's a list of some "trade friendly" bands...
http://wiki.etree.org/index.php?page=BandAbbreviations
And another (a lot of overlap though)...
http://bluegrassbox.com/notrade.php
These recordings come into existence because some bands allow taping at their live shows....
http://btat.wagnerone.com/