Cardas has spade to banana adapters too. Actually, I think they list them as their banana plugs, but they do accept spades.
http://www.cardas.com/content.php?area=oem&pagestring2=Bananas&pagestring=Bananas+(closeup)&content_id=2&part_id=13
http://www.cardas.com/content.php?area=oem&pagestring2=Bananas&pagestring=Bananas+(closeup)&content_id=2&part_id=13