In case somebody may someday need to make some or just be interested.
I have four Mark V windshields, and between them they yielded just two unbroken BD.1889 special bolts that hold the windshield frame into the body.
They are #2BA thread x 1/2" long, with a 7/16" square x 1/16" thick head, which appears to have been made as a separate piece and welded to a stud. I can see a faint circle on the top side of the head which I presume is the end of the stud.
I made my new ones the same way, out of stainless steel, with a #10-32 UNF x 9/16" long stud through a 7/16" square of .062" thick stainless sheet stock. Threaded in so they would hold straight, then welded on the top and faced off.
It was also a surprise to find five round ones. I have no explanation other than somebody got creative, though how they expected them not to rotate when you tighten the nuts is a mystery.
The Mark V saloon uses 8 of these, 2 on each side, 3 along the bottom and 1 at the top center, though for some unknown reason the DHC section says 11. There are cutouts in the top and bottom frames to get the top and bottom bolts in and out. But you cannot get the side bolts out there; they won’t slide around the curves at the corners, because the slot in the frame is distorted by the bends. The only way to get the side bolts out is to separate the top and bottom frames.
To keep them from sliding they were held in place by some sort of soft putty.