MB uses 285/50/18 on one of the early M-class AMG models. Those might be available and I think they would fit. They are a match size-wise as well.

When I went out on Fraser Island the ruts were phenominal. Not sure I'd put my 4.8 out there. Great fun, rented a Range Rover and we went all the way to the ship wreck and back. One of the best moments when we had a couple of weeks in Australia.

__________________
2003 4.4i black ext./black int./black headliner (kid's runabout)
2014 535d X-drive, M package, silver/black interior

Sold but not forgotten:
2009 E70 35d, black ext./black int./black headliner (sold 2021)
2006 4.8iS Le Mans blue/cream int./black headliner, SOLD in 2012 sadly...

Other hardware:
2015 Cayenne S (wife's new DD and definitely wroooommmmm)
2016 Tundra 1794 edition crew cab, luxo hauler
2005 Tundra crew cab, weekend hauler. Sold after 150k very happy miles.