The 1951 Buller Record, unsupported as it is by herbarium evidence, I would not accept. No one that I know has seen this distinctive plant in a natural state in the South Island, and the Buller is now fairly well known. As far as I am concerned Rhabdothamnus is endemic to the North Island, and I won't believe otherwise until i see good evidence in the form of clear images supported with herbarium specimens.
Nw, Makara, Smith Creek - well its a long way up, if walking from Makara up stream, then look on the western bank on the cliff faces in a small forest remnant I recollect. There is not much - I found it in pouring rain and never went back there but I gather the Department of Conservation (Wellington) relocated it there - so ask them for more details.