It seems these birds are dangerous and hard to keep in captivity. This is from Wikipedia...
The cassowary has solitary habits and breeds less frequently in zoos than other ratites such as ostrich and emu. Unlike other ratites, it lives exclusively in tropical rainforest, and reproducing this habitat carefully is essential. Unlike the emu, which will live with other
sympatric species, such as kangaroos, in "mixed Australian fauna" displays, the cassowary does not cohabit well among its own kind. Individual specimens must even be kept in separate enclosures, due to their solitary and aggressive nature. Territoriality is one of their most important characteristics.
It doesn't sound like it would be easy to keep them in captivity. How would you even breed them?