Interesting! I'm seeing some offer on ebay, but first of all I need to find the right diameter for my Bernard Watchl 18x24...
Here a picture of this camera:

Click image for larger version.  Name: WhatsApp Image 2019-11-08 at 10.27.32.jpg  Views: 19  Size: 56.6 KB  ID: 197389

Click image for larger version.  Name: WhatsApp Image 2019-11-04 at 15.00.45.jpeg  Views: 20  Size: 60.7 KB  ID: 197390

unfortunately I haven't the camera with me now, so I'll wait...