IIRC, that is off his ST1100. You might be able to go to the local motorcycle salvage spot in your area and wander through the bikes to see if any fender extension from a Concourse, ST 1100, or maybe some of the full size touring bikes would work. A little custom-fitting, some pop-rivets, and voila' , a masterpiece.
Just 'cause I had it laying around, (and I didn't have an extra fender from another bike to modify), I used the back wall of a de-humidifier catch bin from a clapped-out unit.
The material was easy to work with, the color is dark enough to be all but unnoticeable, and uses the stock hardware that is for holding on the rear reflector.
I just have to lift the bike a little higher when removing the rear wheel than I used to, in order to clear the lengthened fender. No problemo, and it's free!!
Just a couple of inches makes all the difference :bigeyes: ...............(waiting for TWN)
This isn't a very good picture, but I added this extension made with some Buna rubber. I first made a pattern that followed the original contour of the fender and got the right shape. All the hardware was painted black so it disappeared.