I picked up a couple of pairs of the old glass knobs years ago but haven't used them yet because I couldn't think of a way to fit them and make them look good. The small set screw which holds the knob to the shaft going through the door looked ugly, in my opinion. Plus, the small circumference where the shaft comes out would look odd going into anything but a very slender shank.
I'm thinking now, though, that perhaps a plumbing coupling chucked into a drill press or lathe and filed down to a similar shape would be the solution. And maybe replace the set screw with a brass pin which could be filed flat. (Or steel if the knob is mounted in a steel or iron base)
Good luck with them.