My 02 WRX wagon has been replaced with a stock 07 Wagon ... I miss the simple spoiler of the WRX, and some of the power/convenience bits. I was passed on a road trip to Aberdeen by a wagon with an interesting spoiler, and I'm now thinking about options for a simple spoiler kit. I did enjoy the 30 MPG on the 560 mile round trip.
For sale section? You might have better luck in the General Section of the forums. Just trying to help.
Here's a thread from nasioc that has a few interesting wagon spoilers. For price and availability your best bet would be oem. If you go oem and install it yourself post up some pics and a how-to for others. http://forums.nasioc.com/forums/showthread.php?t=569818&highlight=wagon+spoilers