There used to be laserdisc rips of the original trilogy on bittorrent. That is about as close as you'll get.
Not true! There are much better ones available! As an Anonymous poster noted below (and deserves to be modded up!) you should look for Harmy's "Despecialized" versions. Much of the source was actually taken from film and it looks really good at 720p. Look for version 2.5 of episode 4 and version 2.0 of episode. His current version of Jedi isn't quite as good yet, but hopefully a better version will be out soon.
Some info here.