I am making a zoo design on my computer, and some of the species I have incorporated are rare, very rare, difficult to keep, and above all difficult to acquire. So I am wondering, how can a zoo in Europe (in real life) get hold off, and then keep successfully the following mammal species, some of which I have included, and some of which I am considering whether to still include in my zoo design?
-Golden snub-nosed monkey
-Coquerel's sifaka
-Indri
-Proboscis monkey
-Red-shanked douc langur
-Platypus
-Sea otter
-American badger
-Pronghorn
-Commerson's dolphin
-False killer whale
-African golden cat
-Zebra duiker
I know this is a kind of animal list that causes some zoo nerds to salivate

However, even though I am a dreamer, I would like to know how to get hold of these treasured species, because I want to follow my dreams. I want to realize, manage and own a zoo (or several zoos) some time in the future, and then information about this would be very helpfull
Like others have said, you may have significant problems acquiring any of these animals, especially if you were thinking of trying to get them right off the bat. Even fully established and prestigious zoo collections cannot keep some of these, the indri and platypus coming into mind specifically. Realistically, whatever collection you may start is probably going to have very basic species that are not hard to acquire; by caring for these species successfully and proving to other zoos that you meet animal care and financial success standards, you can establish yourself as part of the zoo community and gain access to rarer species.
However, treating this as either hypothetical or as a long-term plan, I thought I could make some suggestions on species you could hold instead:
In place of
golden snub-nosed monkey, you could have
Francois' langur. This is also a endangered tree-dwelling monkey native to China, and there is a captive breeding program already in place for this species. The program has few participating European institutions, so I believe the program is based in the US, but that could change as availability for the species goes up!
Instead of
Coquerel's sifaka, try
diademed sifaka. This is the species being kept in European institutions right now. Availability will be very low until breeding is more successful and the population grows, but hopefully they will be easier to obtain in the future.
In place of
proboscis monkey and
red-shanked douc langur, you could hold
Francois' langur,
silvery lutung,
lion-tailed macaque, or
Sulawesi crested macaque. Not quite the same, but proboscis monkeys will be pretty much impossible for the near future and there are few douc langurs left for you to claim outside of wild-capture.
Instead of
sea otter, look into the possibility of obtaining
giant otter, an entertaining, fascinating, and endangered species of otter that we are desperately trying to grow a captive population for.
Replace
American badger with
European badger. Gotta be honest here... is there really much of a difference? European badgers will be easier to obtain in Europe. If it matters to you, it's probably not hard to acquire a badger in the States; they aren't rare and easily become pests to farmers.
I wouldn't have said
pronghorn would be an issue, but I wasn't aware of any problems breeding them in Europe until Chlidonias mentioned it. If that's the case, perhaps
saiga? Can't really help you there.
Instead of
Commerson's dolphin, use
bottlenose dolphin. Instead of
false killer whale, try
beluga. I am neither supporting nor condemning the keeping of cetaceans in captivity; I am simply making a suggestion based on species availability and husbandry experience.
Use
caracal in place of
African golden cat. They fill a similar niche, especially in the eyes of the public, and caracals are far more available in captivity.
Use
red-flanked duiker,
black duiker, or
yellow-backed duiker in place of zebra duiker. Not quite as striking in appearance and duikers don't seem to be as common in Europe as in the States, but an import should be possible. If you're looking for a more exotic ungulate from the Congo,
red river hog is widely available, and there are breeding programs for
bongo and
okapi.
Again, your collection when you start out will probably be more low-key: lemurs, turtles, parrots, hoofstock. A lot of native animals or common exotics. But starting with these easier-to-care-for species would probably be a good start to building a fully-fledged animal care institution.