I've yet to see another WRX out there with these parts on it, so I looked into things a little more. The Parts Brochure for the 2015 WRX and WRX STI lists them as such. I also added MSRP prices on them.
STI Under Spoiler - Front (E2410VA000) - $399.00
STI Under Spoiler - Side (E2610VA000) - $499.00
STI Under Spoiler - Rear Quarter (E5610VA000) - $335.00
Now, obviously these parts are a bit pricey. Putting that coveted STI logo on anything pretty much doubles it's price tag. However, there's not much markup in these. Both local dealerships that I called and SubaruGenuineParts.com were only listing these parts with a $20-$40 discount at most. The dealer cost isn't too far off from MSRP.
Presently, if you're ordering a WRX from a dealer, they do not have the option to add these parts on from the factory. This may change, but as of this post (May 2014), that's what it's like now. Unlike most parts, like the Performance Exhaust, these can only be ordered as parts through a dealer and then added on later. I'm not sure why this is, although I would imagine there might be a risk of damaging these parts being loaded on and off of transports. Pictures and part numbers are listed below of each part.
|STI Under Spoiler - Front (E2410VA000)|
|STI Under Spoiler - Side (E2610VA000)|
|STI Under Spoiler - Rear (E5610VA000)|