Richard,
It wasn't my intention to cry in my beer, just to inform you (and others) of my experiance. If its not standard, you're on your own with most shops, who after all are in business to make a living. Good luck.
George,
I'm past caring about sliding side curtains now, but you are right- the boat shop extrusions are the only special pieces that would be needed to make a set. Once you have those pieces, and a template, it would just be about cutting two pieces of polycarbonate and tig welding the frame.
I will add that I think have come to believe that the point is moot, unless you have a Beck or Intermeccanica. Most side curtains are made of canvas because the shape of the opening on cars w/o a scissor top frame varies from car to car, and to a certain extent from side to side. In other words- no two CMC, or Vintage, or JPS cars are alike, and therefore hard side curtains are not really suited to mass production. I watched in mild amusment several months ago with the guy who made his own curved side curtains, and was taking orders for production. I think the whole thing just kind of fell apart once he took a good look at it. Hard side curtains are possible, but you better know a good custom fabricator, or get get ready to fabricate them yourself. I did. The funny thing is- once I turned my attention to the soft-top, I got the canvas side curtains to seal up better than the hard ones ever could have. It isn't all that hard to VASTLY improve the seal and usability of the standard VIntage/ JPS/ CMC soft-top/ side-curtain package. I posted the details in a thread last fall. I took the car out today- 30 deg, and it worked great. I wish I knew then what I know now... I'd be spending money in Mexico (or maybe San Paolo like Carey).