Ordered the ducts online from one of the stock car (nascar) suppliers, they're about $20 a piece and come in black or clear. I get the clear and then paint the backside so it stays shiney and scratch proof
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I have only seen them in carbon at one place... I think he quoted me $200 a piece and said about a month and a half wait....
http://www.gospitzer.com/prodline1.htm