I am not sure why you would want that extremely weedy, aggressive herb but as you come from Auckland you can find it easily enough in the Waitakere Ranges, or around Ihumatao - such as at the stonefields where its abundant on the scoria and basalt blocks of the old quarry pits. I'd be worried if the seeds of Geranium robertianum were being sold. Another area you can try is the King Country or Waro - just look on any limestone outcrop.