Ah - I was just about to ask if it had ever happened (a Kiwi 1-2-3, that is); I couldn't think of such an occasion and was getting too sleepy to research it further!
The best chance was at the Canadian Grand Prix 1968. Amon, Hulme and McLaren toured about 30 laps in that order. Naturally with Amon's luck the final drive on his Ferrari gave up, and they finished with Rodriguez in 3rd place,
These 3 did make up an all Kiwi podium in Can-Am a couple of times in 1969, when Amon drove the 612P Ferrari.