I have found boat supply houses to be a great resource for hard to find hinges. attachments really almost anything. And I have seen wind wings at them. The motorcycle shops have some that mount differently than ours check those as well. If you side or post a picture of your needs I’ll check the shop there might be something I can lift for a brown bottle so you can attach the normal ones.

 Last night while surfing I found a you tube vidieo of a Duchess with about a two second shot of the horizontal wind wing mounts you described. They must be very rare but at least we know they did exist.

 I have also seen non-adjustable wind wing mounts made of alluminum flat stock  1/8 x 1/2 inch cut into 3 1/2 inch lengths and bent to the desired angle. The alluminum strips as well as the plexaglass  or lexan are available at home improvement stors. This would allow you to use the existing holes in the windshield frame, but could interfere with the side curtains depending on how they fit to the frame. By the way, this type of alluminum will polish out almost to a chrome like finish.

 Another of my ”cheap” alternatives.