fraid i can't answer specifics on which zoos are earmarked for tiger imports, but it is all based on which tigers are recommended for breeding/pairing. if for example a zoo held a tiger that was called apon for breeding but the zoo who owed that tiger had not the facilities to breed, its highly likely that the zoo would give up that specific animal to a zoo who did have the facilities (and who would therefore also aquire the animals recommended mate). in return the original zoo would no doubt be supplied with another cat(s) to display and hold.
a lot of shuffling goes on.
in regards to snow leopards i can tell you that melbourne is about to import a fourth snow leopard, to pair with their younger female. the older cats are on the way out. the national zoo also holds a female snow leopard (ex-mogo) who i believe they are trying to secure a mate for.