They are just a larger, greyer version of the other Grass baboon subspecies, so I can't see anywhere deliberately importing them when other subspecies are already available.
There are places that seem to enjoy having the unusual (such as Prague and Plzen), so I wouldn't rule it out entirely. It's obviously not likely to happen any time soon, however.
As Maguari says, its what's available. Usually one place starts up by getting a small 'splinter' group from another Zoo.
For many years there were no Guinea baboons in the UK until Port Lympne, and later Edinburgh, received all(?) the animals from the Paris Zoo colony, while that zoo is being completely renovated. Previously the last Guinea baboons in Uk were probably at Windsor Safari Park.
Edinburgh, Colchester and Howletts alll have Geladas now, another species that was absent from the UK for many years.
I've never seen Chacma Baboons in the UK- I've only seen them once in a zoo at all- somewhere in Europe but no memory of where.
This Hamadryas island looks as if its been upgraded in recent years with more rockwork, tree stumps etc added, whereas previously it was very bare.
Auckland Zoo got its stock from Taronga Zoo interestingly enough, and I believe they had many births over the years, with overcrowding being a major issue. The zoo stopped breeding this species in the 90s though, and they are now down to one male, which they are transferring to another zoo (this might have already happened). There are now only two individuals in the country, and the species will die out here in the near future.
Auckland Zoo got its stock from Taronga Zoo interestingly enough, and I believe they had many births over the years, with overcrowding being a major issue. The zoo stopped breeding this species in the 90s though, and they are now down to one male, which they are transferring to another zoo (this might have already happened). There are now only two individuals in the country, and the species will die out here in the near future.