As I had posted in my response from last March (Post #5), forum member gmadrid found the J-3231980 flex duct offered by Crown Automotive. While not exactly the same as the Ford flex, the dimensions were very close to the Ford duct, and he reported it fit perfectly. The Crown Automotive site lists the dimensions as 2.5' X 3.5" x 12.5". The Ford service flex hose, D3OZ-9A624-B, is 2 5/16" X 3 11/16" X 11".
There is another Crown Automotive flex hose I found recently, J-5359272, listed on their site as 2 5/16" X 3 11/16" X 18". There is a discrepancy in the length listed (Isn't there always) as a couple of sites I found listed the J-5359272 flex hose length as 12-13". I saw listings by part number on sites such as eBay, Summit, Jegs, etc. You may want to check by the Crown part number if you have a favorite online or local parts store and see if they could verify the dimentions.
Since from an earlier conversation, you had verified that your '72 does have the NOX system, a hard plastic duct ran underneath the battery tray to the front of the vehicle. The Ford part # is D2ZZ-9A624-A (Engineering ID # D2ZF-9A624-AA, AB, AC). This duct is listed for all V8 applications, 302, 351C (H, Q, R).
If no one on this site has one that needs a new home, I would check with Mike @Motor City Mustang. He is a forum member and site supporter, has parts cars, and has an E Bay store.
He can be accessed under "Forums" > "Market Place".