What are you going do with 50kg dumbbells?
Not many exercises at that kind of weight.
And very expensive too, for the limited use they would get.
Unless you are looking to get a whole rack full of dumbbells, why not get some adjustable spinlock dumbbells?
You can get them up to almost 60kg each.
We sell a 100kg adjustable set (up to 50kg each dumbbell) for $295 from Sydney, $60 del to Adelaide.
You may get a better deal locally or Melbourne prices are quite competitive.
Or check out eBay or Trading Post online for some good deals.