There may be a place holder that Amazon has up on it. Apparently they haven't received their shipment from Motorola yet on the 16gbs yet.
http://www.reddit.com/r/MotoG/comments/3ezrln/anyone_else_preorder_the_16gb_from_amazon/
There are links to the 16gb in there. Read more for more info.
Link to Amazon listing: http://smile.amazon.com/dp/B00ZQVSKS2