That's odd. I've purchased from Get Games before. Do you live in the US?
Try Green Man Gaming. They currently have a 25% off voucher for digital purchases.
http://www.greenmangaming.com/
I live in the US. It lets me add to the cart but at checkout it says game is not available in my region or something.
I also tried GMG, doesn't let me apply the code for this game (guess it doesn't work on preorders)