That's right! They are doing it. And it's not some unauthorised released or fan-made soundtrack. It's the official Supernatural soundtrack, featuring some of the key instrumental tracks from season 1 to 5.
I couldn't believe it when I first learnt about it, I have to look at my sources to confirm it. And it's real! You can pre-order it from Amazon. You can see the full track list here.
I am not sure if this will be available on iTune. It's so cheap, like $8.98 US. Normally, a track from iTune is around $1.69 AUD. If it's available on iTune, perhaps you can only download the entire album and not the individual tracks. Anyway, if you know this is available on iTune, please let me know.
Amazon is referring "this product is manufactured on demand when ordered from Amazon.com", meaning "this recordable media is used to manufacture titles on demand, as fully authorized by the content provider." Read more here.
If I am understanding this correctly, the way it works is that if you order it, they will pop all tracks on a CD and ship it to you. The quality is the same as a CD. It's not the usually movie or TV soundtrack (hence the price). I think they are doing this for the fans only, which is fantastic!
The soundtrack is available on 7th September 2010.