I think you mean one like on this webpage:
http://www.eenwieler.nl/product.php?idObject=696
I'm sorry I don't know how you would call it in English or where to buy it in Amerika. Maybe it will help you further because now you know which company makes them
Oh after a bit of googling I came to this. maybe this helps you:
http://www.williamsmagic.com/index.p...ducts_id=15249