I am quite impressed with the website. Been a waterfall fan myself. I felt I finally found a group that understands what I like!
If you catch a train from Auckland and Wellington, there are many nameless waterfalls all the way, especially after Tongariro National Park, and Wellington (All the way till the end, there are waterfalls 5km from Wellington rail station) big or small waterfalls en route beside the railway line, some aren’t as spectacular as the ones in your book, but still special!
Also between Taihape and Hunterville, the train mandering along the top of Rangitikei river valley
Some part of this stretch you get to see waterfall all along the river valley! there are spectacular waterfalls along Midland mainline (Tranz Alpine train) as well in South Island.