I found mine on eBay...but also watched the classifieds on this board. The GN intercoolers (stock) will work also. They supposedly have less fins per inch, but are the same external dimensions. I have a low mileage GN IC in my TTA right now.
I have a stock TTA IC that I would sell, however, it needs to be repaired. It leaks at several connections between the tubes and the tank. I am not sure what it is worth?