The Amazing 3 (Wonder 3 or W3 in Japan) is a 1965 Manga series created by legendary manga writer Osamu Tezuka (Of Astro Boy and Kimba the White Lion fame). It focuses on a trio of aliens disguised as a duck, horse, and a rabbit, who meet a boy on Earth and learn things about the boy's planet. An anime adaptation of the manga started airing on Japanese and American television in 1965. While the Japanese version of the anime can still be found on the Internet, the American dub is very hard to find and is rumored to be destroyed. The last time the English dub of the anime was ever aired and seen on American Television was during the 1970's on KCOP-TV as reruns. A few episodes of the English dub were uploaded to YouTube sometime in 2013 or 2014, but later got removed for unknown reason. 12 episodes on original film negatives were found in the KCOP vault and were trying to be sold on eBay for $24,000 a few years ago. Some episodes are also available on grey market DVD-R.
The only evidence of the English Dub existing outside of the English episodes is a video that was uploaded on Youtube on January 13, 2013 titled "Captain Bunny's Greetings" uploaded by Youtube user "unclesporkums". The video contained a two minute audio clip of the character Bokko (Called Bunny in the English dub) giving a greeting. The audio itself is from an unknown old website that may no longer exists according to the uploader. The video description did mention that it might be an impersonator of Corrine Orr who is the English voice of Bokko but is difficult to tell due to the poor audio quality. The video later got deleted at an unknown time.
First English dubbed episode: https://www.youtube.com/watch?v=OKU7tOfJjto