I've seen more than one enthusiast roll their own.
As the urban legend goes, the method used by the factory to roll the fenders was crude, using a 3-foot long pipe, 2-inches in diameter. With the fender and tires mounted, one leveraged the pipe at the top of the wheel well, and pressing downward, the wheel is then rolled forward and back to create the fold.
I'm aware of at least two restorations, where the "standard" fender lips were rolled by the owner for some sense of authenticity.