I have seen them on Ebay.
Here are the things that go behind the headrest.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7917681690&category=33645&sspagename=WDVW
Your dealership should have the pieces to secure the wind deflector, I heard from a Porsche tech they break often.