British Pathé has released a large number of news reels to YouTube. Many zoo films from 1930s on included: https://www.youtube.com/user/britishpathe/search?query=zoo
Have a hunt through this lot, my favourites were Roland the elephant seal at Berlin zoo, looked like he was kept in the elephant house and a trio of "Malaysian tarsier" at London zoo, ssaid to be the first tarsiers seen in Europe. Search Results: 'zoo' - British Path
I must have a look at these YouTube ones. My favourite British Pathe (I do not know how to get an accent!) films are of Flamingo Park, especially the one featuring Winnie the Pilot Whale (although that piece of film is part of a compilation).