From what ive heard they arent for sale anywhere and only come on the JM strats (big dippers that is) so direct from fender may be the only way, maybe try talking nicely to your local music store and see if they can get them for a "repair"
With regards to what they do, they basically scoop the mid range out, this may sound like a bad idea, but they hold a lot of versatility and carry a really beautiful fender clean sound. Check this video out:
http://www.youtube.com/watch?v=HZlwLYhZ1Hc&feature=player_embedded
hope this helps
