Hutt pet has them every now and then.
If you want to catch them I heard that there are some ponds on the eastern hills with them, but the hike is too much for my curiosity.
My friend has a pond on their farm with them, but he's in Horokiwi and the frogs there are not cute little whistling tree frogs, I think they are bell frogs coz they get quite big and noisy in the summer.