Hind sight is 20/20 eh? I see ducts on ebay fairly regularly. I think several years might work as well as car ducts may work too. If not an exact match they're probably close enough to be able to make them work with a bit of effort.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.