Pennzoil Plat 5W50 is available closest to Australia is New Zealand, I spoke to Pennzoil and reckon due to marketing will not have it in Australia which i am not happy about. The 5W40 Pennz Plat is just too thin for some of us to use, especially in Holden and Ford 6's and 8's.
A good 5W50 to try is the Penrite Everyday Synthetic 5W50. It is a full Group 3 oil, SM/CF and has about 1040ppm of Zinc etc. Other additives i do not know. It is listed as Full SAPS for a SM rated oil. Also comes in 10W40 so good for alternating between the seasons. I am inclined to try is as it retails always for $50 max, $45 some places. Good consistent price for GRopu 3 in Oz, when everyone else is selling it around $70. Then again, Penrite sell their PAO oils for that much. Maybe their possible use of recycled base stock (not that its an issue) helps them lower the cost.