With Zabriskie Point, where you saw it is much more valuable than how. It wasn't released in its original form in many countries. But unlike The Passenger, I don't think that any reports of missing reels from the "original" exist, though that can change. (The soundtrack, a key aspect of the film, was altered for the U.S. release.)

A new print of the film by Warner Bros. played a couple of months ago at the Brooklyn Academy of Music during an Antonioni retro, so there's hope.