Kristian Brown, a lucky librarian at the University of New Brunswick in Saint John, came across a Revised Fourth Draft “Shooting Script” of Star Wars while digitizing some of the library’s content.

Readers of this site and script connoisseurs are familiar with all the changes this draft incorporates. The article mentions things like the using of the name Starkiller in place of Skywalker and so on. The article’s description matches what we know about the fourth draft so this looks like a rare find indeed.

Kristian Brown, a librarian, came across what appears to be an original shooting script for Star Wars when he was digitizing the university's science fiction collection of zines, pulp magazines and novels. (Elke Semerad/CBC)For Brown, the biggest thrill was reading how an original scene featuring Harrison Ford was meant to be.
When Lucasfilm re-released the films in 1997, the special edition altered a scene where Han Solo is met by a bounty hunter.
In the original, Solo fires at the alien, killing it without warning. The 1997 version changed the scene to make Solo look as if he was acting in self-defence. A change which incensed fans.
“I’ll tell you one thing, right now,” Brown gleefully points out.
“Based on the script, I can tell you 100 per cent, Han shot first.”

Source: CBC News