I just got a new reproduction "Ducktail" spoiler off of ebay. Just like the original with the exception of the mounting holes. This one mounts from underneath the decklid and is smooth. Good price, good quality.
The reproductions are made of Fiberglass not ABS plastic (same stuff that is used to make the Sharktooth grill). All I have is the original one, never had a repo one yet so don't know how they stand up over time.