Arm yourself with some photos and dimensions of what you need, and take them and the bike to one of the specialists who advertise in the Classic press. I believe that the original Silk exhausts were made by Newton and Sulley, trading as “Granfab”, in Bulwell, Nottingham. The partnership split up years ago, but Andy Newton is still trading on his own, and he can do a very good job. He MIGHT still have the original drawings/patterns. The only snag is that he can be very slow in coming up with the goods. I can’t find his phone number, but another member may have it. His workshop is situated behind Glenn’s Motor Caravans, on Cinderhill Road, Bulwell, Nottingham.Hope this helps!