4 Porsche Cayenne Center Cap Sil 911 993 996 997 Boxster New Four Piece Set | eBay
I got mine from ebay and they were great payed $25 for them and they are tight as can be. Unfortunately the seller I got them from does not have them any more but they all get them from china so the link above should give you the same results and they are located in the US. I pointed the tips of the shields to the stem valves and they still are pointing in that direction.
Here is a link to my post.
http://986forum.com/forums/general-discussions/46230-new-center-caps.html