A few years ago I got one from Rockautos.com in the US, was around the $100(ish) mark. They have different USDM model numbers, but the part numbers matched up.You just need to to go through their database of cars to see if you can find the correct one. At the time, mine was for a V7 STi.. don't know what you need.
Also, if I remember correctly, there is a difference between front and rear (pre- or post- turbo). The one I got was front (pre-turbo, in the exhaust manifold). From the image above, it was the lower one. The big white connector on the end fit through the 'O' end of a standard 17mm (I think) ring spanner, so it was easy enough to install myself, once you get all the heat-shielding off (which was a pain).