Some rare mammals kept in Japan:
Tasmanian Devil at Tama Zoo
Quokka at Saitama Children's Zoo
African Manatee at Toba Aquarium
Dugong at Toba Aquarium
Amazonian Manatee at Attagawa Tropical and Alligator Garden
Johnston's Wildebeest at Izu Animal Kingdom
Long-tailed Goral at Kyoto City Zoo
Douc Langur at Zoorasia and Shunan Zoo
Proboscis Monkey at Zoorasia
Purple-faced langur at Chiba Zoo
Golden Snub-nosed Monkey at Kumamoto Zoo
Yellow Baboon at Hamamatsu Zoo
Moor Macaque at Tobe Zoo
Formosan Macaque at Kuragaike Park and Tobe Zoo
Eastern Bamboo Lemur at Ueno Zoo
Bearded Saki at Higashiyama Zoo
Thanks for listing it!
Just a couple of things I'd like to point out
The gnu at Izu Animal Kingdom is an eastern white-bearded wildebeest, so it is not rare!
Also, the Eastern Bamboo Lemur at the Ueno Zoo died just recently.