Can you confirm the size of the duct you need ID of the duct would be the most helpful.
Here is one source
http://www.cgfordparts.com/Early_Ford_Parts.htm
online catalog for 32-56 car and PU do a search for "CLOTH HEATER DEFROSTER HOSE" for the different sizes.
Pattern 12 Chevys use 2 1/2 ID duct.