They require large amounts of space to roam and a specific diet of soil invertebrates (like worms and grubs), making them incredibly difficult to maintain in a home setting.
Since you can't buy one, you can "adopt" or support them through official conservation channels: buy a kiwi bird
Kiwi are flightless, nocturnal birds native only to New Zealand. They have the second largest egg per body weight of any bird. National Zoo Facts and threats to kiwi - Department of Conservation They require large amounts of space to roam