Brachaspis genus itself is endemic to South Island of New Zealand. So there is no question of occurrence of robustus or any other species outside New Zealand.
There are three species of Brachaspis. They are: B. nivalis, B. robustus and B. collinus. All are endemic to the high country of the South Island of New Zealand. All are flightless, one (B. robustus) has the second to highest threatened species status in New Zealand (Nationally endangered).