I can't say if there is such a product. I have rarely seen actual USB ports on a motherboard. The more common ones are 19pin headers which would use this this type of bracket: http://www.amazon.com/KingWin-Bracket-Built-In-20-Pin-KW-PCI2USB3/dp/B00BTYOKXO/
I'll keep an eye out. If you need more usb 3.0 ports, I wonder if it would be cheaper and faster to just get a new pcie card, or a hub.
EDIT:
I found something simular, but it's not quite what you need... it has a usb 3.0 B type connector in the back http://www.picco.nl/catalog/product.../4568/osCsid/r2h86kb04gqq4epmpopriiibb7rnb1aq