There is a DVD box set release that came complete with the unaltered original films as bonus material.
Each movie comes as a two-disc set—one disc is the 2004 remastered version of the film, while the second disc is a version that captures its original theatrical presentation.
If you heard that this 're-released' trilogy was not so good. It's because it used non-anamorphic video sourced from the 1993 LaserDisc releases. It's just not good as the restored 1997 Special Edition (Gold or Silver box) and any subsequent release, which you should avoid because it include many changes from the original theatrical version.
After that, I think your best bet would be to check garage sales or to go on Ebay for the first VHS release of Stars wars or The "1995 VHS THX Edition" (Black box).
The 1993 laser disc Star Wars Trilogy: The Definitive Collection would be also OK, if you have the player to use it, but you wont have a better image than with the DVD, as the source is the same.
But, be notified even those versions has some small changes, I recommend to check the wikipedia page about List of changes in Star Wars re-releases to pick the release you want.