As of a few yeas ago (and I assume this is still true) they should have at least one off-show breeding pair of every species (and, to my knowledge, more than one of every species except Brolga).
That is interesting! I did not know that. Do you think they will try to import more Brolga to pair with the offspring they produce? (I suppose it will have to do with space. I don't know if they want to share the Brolgas with anyone else or not.)