72 demon 3/8" fuel line?

Are you looking for the line from the tank to the fuel pump? I used Year One stainless 3/8" on my 72 Demon and it fit very well. They also have a mild steel 3/8". Here's the links (click on part numbers):

Part Number: QRA14TS Mild-steel full-length fuel line for 1969-1972 Valiant, 1969 Barracuda, 1970-1972 Duster, and 1971-1972 Demon models, 3/8" line.

Part Number: QRA14 Stainless-steel full-length fuel line for 1969-1972 Valiant, 1969 Barracuda, 1970-1972 Duster, and 1971-1972 Demon models, 3/8" line.