Yes, it looks like all over the country just got in SG Ultra Magnus, and yet it is not listed on their site either... I guess it was shipped out from the Hasbro warehouse like SG Blaster to each eligible retailer, but some of them never had it listed for pre-order, and as such didn't have an official release date to hold it to.
It is being sold for $99 at JBHifi, which is $5 cheaper than Amazon Australia, and 5 weeks earlier too.
Legacy Motormaster is now being found at other outlets, such as Toyworld and JBHifi... so the "BigW exclusive embargo period" might now be over, and it is shipping out to other retailers. I would imagine that it will show up on Amazon Australia soon too.
Plus... Legacy Metroplex - now out here, at a Toyworld in Victoria first... but the release date at EB and Amazon is mid-September, so a little bit longer to wait if you want to save a little bit on the price.