I was searching just for a cloth cover the other day and ran across something similar on ebay....
Is this what you are talking about? Looks like for 07-04...
Boxster 97-04 Duraflex Tonneau Cover Maston | eBay
Sold here direct by the company:
1997-2004 Porsche Boxster Maston Tonneau Cover : 105876 Duraflex by: