I don't think the stock windblocker makes a real big difference, but if you are after a genuine Honda one, try this place and save some cash:
http://www.handa-accessories.com/s2000-03.html
I would suggest installing this product instead.
http://www.ricks2k.com/products/aero.php
You may also be insterested in these:
http://www.ricks2k.com/products/aero...stWindBlockers