There is not anyone making one commercially. A restoration shop with metalshaping capabilities can make you one. The concept is what we call a 'reverse curve', and we start by using a mallet on a sandbag to introduce the initial shape in the sheetmetal. We then use a pneumatic planishing hammer to smooth it, and a wheeling machine to add the final shape.
I am at home and do not have any pictures available to show you but if you are on Facebook, go search for 1928 Ford AA Truck and a restoration project should/will come up showing the basics on how it is done. You should be able to run with it from there.