These are not made aftermarket and it's a ton of work to make them yourself. I have no idea what the quality of these is like, but you seldom see them for sale. Just getting them chromed is around $1200 each. Might be worth looking at....

SW rear smoothie:
http://www.ebay.com/itm/1956-Chevy-S...-/282361189398

Regular rear smoothie:
http://www.ebay.com/itm/1956-Chevy-S...-/282361189377

Front smoothie:
http://www.ebay.com/itm/1956-Chevy-S...-/282367785163