Papa was a rollin' stone...
Sometimes products are available at Gen Con before they hit retail.
This is not all that rare, actually.
For example, The Adventurers: The Temple of Chac was available last year before it was on store shelves, as was the painted minis set.
It probably wouldn't hurt to keep an eye out for it if you're going to the Con on Thursday; if they do have copies available for sale, they'll go fast, to be sure.