I didn't preorder but I'd still like to know where that boxed version can be found. It's only in USA I guess?

Unfortunately this game isn't available as usual retail version. So no boxed copies sold in shops anywhere in the world. Still Dave produced an amount and sold and sent it out himself for a certain amount of time ('til end of July or so).
But he did ship worldwide and I was lucky to get one send to me to Germany :)

But don't give up the hope! As the source in my earlier post says, there seems to be a possibilty that Dave would do this a second time sometime in the future.

Oh I'm fine with the Gog Version. :D