Available from veoh, but I've consistently had trouble with their required downloadable player. Youtube has it online in 13 segments. They ought to auto-play from part 1:
The film itself is not entirely as silly as its name, however--it is instead a meditative and minimalist bit of decent, humanistic science fiction.
DVDTalk calls it "a unique and serious adventure" and says, "Given the year that it was made, Robinson Crusoe on Mars is scientifically very impressive." Bright Lights Film Journal calls it an "underrated film" and says it "encourages the viewer to face issues that are as relevant today as they were in the 1960s: propaganda, war, and discrimination". The New York Times says, "It's good fun all the way." 1000 Misspent Hours has a review.