I have the center piece of the OEM windblocker (hard plastic mesh, not the over the hoops mesh one). It has a small < 1/8 " hole in the middle but works flawlessly. The piece normally retails for > $300. $100 and it's yours. Local pick-up only either downtown Seattle or Redmond. You'll need to buy either the roll cover hoops or the deflector mounts.
Cheers
For reference (not the one I'm selling):
http://www.ebay.com/itm/OEM-BMW-Z4-W...item3a4f50296c
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'12 Nero/Rosso 500 Abarth
'07 IR/SBL ///M Roadster (GONE), '08 Tornado Red Triumph Daytona (GONE), '09 BRG/Cloth 6MT MINI Cooper S (Spontaneously Combusted), '06 IR/IR ///M3 Convertible 6MT (GONE), '04 JB/CR Z4 2.5i SMG (GONE)