I have a total of six for my eight cars. Two came w/ the car (both factory aerokit cars), one is a fiberglass top for my Spec Boxster project, one I bought for $800, another I bought for $1,000. The last I received in trade on a drug deal w/ 78F350 when he stole a 2000 Boxster. He stole the car, I delivered it.
No, none of them are for sale. I'm still looking for two more.