It was just "released" like the 15th of last month, maybe it hasn't worked it's way through the supply chains yet. Or maybe it was killed off already, seeing how it was like a year late  
My google-fu came up empty too...

Kinda a goofy idea though, and it really doesn't solve any problem as you still need risers. Probably more expensive up front, plus a lot less resale value down the line. There are plenty of options for 6 gpu boards now, for under $100 even.