The Cinemated Man offers it online:
Veoh has the film available online, but you have to download their horrible player.
Moria says, "Symbolically, THX 1138 is a film about finding human individuality inside an impersonal and automated world." Roger Ebert says, "... as a work of visual imagination it's special". SciFi.com has a review. The New York Times says, "Mr. Lucas's film looks like a slightly old-fashioned anxiety dream—but if you can accept that (and you should), it becomes very potent material indeed." The Rolling Stone review gives it one star and calls it a "ponderous period piece". SFSignal likes it. Christianity Today has discussion questions. DVDTalk regrets that the original release is unavailable, saying,
THX 1138 was a superior product of its day, and it's too bad that we can't see it any more. In its place, George Lucas has given us his revised version, adding visuals and augmenting scenes..