Well it just so happens that I was making a fly screen version and took some photos.
I got the channel from a localish company that make the Caterham and Ariel Atom cars but they don't deliver so I had to pick it up. Really hard stuff to find but I'm sure aluminum extrusion stockists can probably get hold of it. Looks like this, has a 9mm channel and the bottom section has a channel for a seal strip.
I made a form from 9mm MDF, put the channel on the top edge, clampped some steel plate with packers around the frame and held it in a vice while I slowly bent it round.
