you mean you want "Dog Transmission (that's what they call it in Japan)" I'm Legacy guy, so I asked my friend in Japan who owns WRX.
this is a website for "dog transmission". it's in Japanese, though.
He said that transmission costs way over $10,000. and suggested to swap to 6 speed gear for GDB impreza to save the cost.
Your thinking fast car. He wants a dual range 4wd ej transmission. We never got those. And in all honesty, if you can get the price right on those you could sell more of them here than you could cars.