VW sold a genuine rear wing through the Genuine VW accessories catalog. You could probably find one at a junk yard or used on eBay, in your stock color; as they were very popular. There are allot of different styles; you just need to do some research and see what you like:
Volkswagen Genuine Rear spoiler
A rear spoiler will make your Beetle look sportier.
Made of a durable, high-quality plastic, the spoiler
is primed and ready to be painted in the colour
specification of your car. Price excludes painting
and fitting. Not suitable for 1.8T & V5.