The most obscure part I ever looked for was this Simplex SJA222 FD. Of course I'm not still looking, so you can disregard this note.
What is so obscure about it is that it is bolt-on mount that bolts directly a hole in the ST, not to a brazed-on bracket. The noteworthy feature is that I started looking as soon as I saw the frame for sale and found one almost immediately.