I have quite an extensive collection of live bootleg shows. I wasn't one to go the local record store and ask for the "behind the counter" look at the the bootlegs though. Back then most were lousy audience recordings. Lousy because the technology at the time was poor.
I began collecting live shows with cassettes of the Grateful Dead, the granddaddies of live concert recording, but really started collecting other artists in the past ten years. That coincides with the internet and better stealth recording equipment. The thing is, some bands encourage recording, just like The Grateful Dead, so there's no need to hide.
There's also the treasured soundboards, where someone records the show from a direct line out of the large mixing console at the back of the room. The sound is usually terrific but may lack in that live ambiance due to little audience sound.
Nowadays you can listen to thousands of live shows for free on a number of websites. Here's a list:
NPR Concerts This archive continues to grow as NPRs prominence as a top notch music site continues. We can only hope it survives any sort of federal budget cut.
Archive The oldest site on the net, this archive is kind of like the Library Of Congress to my mind. It's got more than just concerts too. and yes, there's a slew of vintage Grateful Dead shows.
Wolfgang's Vault Wolfgang was legendary concert promoter Bill Graham's nickname. Obviously this site has a number of shows from the days he ran the Fillmore West and East, but there's also plenty of others. The best part is that there's a smart phone app so you can listen to shows anywhere.
Dime A Dozen This is a torrent site meaning two things; one, you have to download the show via bit torrents, and two, you need to be somewhat tech savvy. The rewards are great though with over 40,000 shows and growing. Plus, an artist can request their shows be pulled if they don't want them available.