Don't know if it was an option or what. They're made of sheet metal. I've seen pictures of a couple of members cars that had them. Maybe they only came with AC?
As an aside to this thread and I was curious about the rarity of these shrouds, I just finished going through all my 65 A Body literature and the only reference I could find for a fan shroud was that it came standard on the trailer towing package. The standard package included special radiator, high pressure cap. 17 inch fan, the aforementioned fan shroud and a yoke-to-hood seal. Other items were required and at extra cost. There was nothing mentioned about a fan shroud in any of the AC areas including the parts catalog. The parts catalog does show in Section 7 (cooling) where the fan shroud is broken down by parts number in section 7-08-0. However, it doesn't even show a picture of it among the radiator/fan areas. Since it was available, maybe it only got ordered when the salesman "pushed" it or when the trailer tow package was ordered. Hard to say.