Enough has already been written on the much maligned special editions of the original trilogy, so I won't write more here. But if you do want to watch the unedited versions, here are a few of your options.
If you're lucky enough to have the original VHS releases (and a player to play them on).
Released in limited quantities, this was the first and only DVD the theatrical versions of the original trilogy. However they fetch a few $100 on eBay and the quality isn't the best, as they come from the laser disc versions.
If you look hard enough you might be able to download the 35mm edit, a fan project which cleans up the original 35mm prints.
You're even less likely to have a Laser disc player than an old VHS player hanging around.
Finally, note quite the theatrical release, but the Despecialized Edition stitches together various sources, removing the edits made in the special editions of the original trilogy.