Amazon has this currently listed as "Temporarily out of stock. Order now and we'll deliver when available. We'll e-mail you with an estimated delivery date as soon as we have more information. Your account will only be charged when we dispatch the item." even though this has been sold out for quite a while.
This has become quite a rare and valuable steelbook, I missed this when it came out a couple years ago, so I ordered a copy from Amazon. Let's see if I'm actually going to get it. Usually Amazon has been pretty accurate with their listings though and they have some older (previously Zavvi or Play exclusive) steelbooks in stock, which have been released years ago, like Michael Bay's The Rock and the 1990 Teenage Mutant Ninja Turtles steelbooks. Both of them are sold by Amazon themselves and not a third party seller and the same goes for The Treasure of the Sierra Madre steelbook.
https://www.amazon.co.uk/gp/product/B00A6W9ASK/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1