I can recommend both Time Has Told Me and Good Job I Kept My Turntable - they're run by enthusiasts and dedicated to putting otherwise unavailable music back in circulation. The guy who runs GJIKMT is extremely scrupulous about only making available albums that aren't on sale any more - I've seen him take down links not only to albums but to individual tracks when he's been notified that they're still out there. At the end of the day it's no different from taping an album you've borrowed from a friend.