Tinbasher has it. Most sell the aluminum due to ease of forming but it's nice to know it's out there.
https://www.snydersantiqueauto.com/p...6988&cat=41643
A person can see that it is formed from sheet steel into a T section in the above link. A person may have to shrink the hidden leg section that is between panel to get he curve. An alternative would be to cut slits in that hidden leg to allow for bending a curve. The model T part is a few inches longer but these were made for sedan type bodies so they only have a little bit of curvature to them. They are a bit more expensive than the aluminum parts.