I swear I saw more at Melbourne.
To think of it, their enclosure was somewhat larger than I remember (going off of the map in the website)
They definitely only have three and have done since Yuska passed away last year. Prior to that, they held this quartet for several years. Melbourne have a large exhibit (opened 1990) and could easily accomodate more. I hope to see more females imported in the near future, which will hopeful stimulate breeding.