Penguins Behind Bars was an Adult Swim pilot that aired only once sometime in 2003. It was about a female penguin getting sent to an all girl prison.
Excluding the promos that have been posted online, the full pilot hasn't resurfaced anywhere, though the script has been leaked by YouTuber RebelTaxi, which he mentioned in his video "Top 6 Unfinished Banned Cartoons & Anime".
Janet Perlman, the creator, says that she no longer owns the short, and CN owns it. she says its up to them to release it.
DVD copies of Penguins Behind Bars are being sold on the National Film Board of Canada's website: http://www2.nfb.ca/boutique/XXNFBibeCCtpItmDspRte.jsp?formatid=51290&lr_ecode=collection&minisite=10000&respid=22372
It is currently unknown whether or not this is actually real or not and won't be till a copy is actually is seen.