For a reference picture, see here (second pencil from the top: black plastic barrel with thin metal rear tail).
https://www.reddit.com/r/mechanicalpencils/comments/1cahnhh/new_pencils/
Differently from its “cousin”, the Faber-Castell Tekagraph 9603 (triangular body), which is much more common (at least the black-body version; there is a green-body variant which is harder to get), the 9604 is some sort of a “ghost”.
Last time I saw it, it was in an Instagram picture by a Mike Windham, whom I swiftly contacted for a possible sale. Unfortunately, the leadholder was already on its way to another collector, who had swapped the 9604 for some Theo Altheneder leadholder that mr. Windham was looking for.
There is also a picture on this forum: the 9604 was part of the legendary collection of Damdeok, “the Korean”; you can see it here (second half of the post): Collection of Damdeok, the Korean - #205 by stu-dying, but please browse the whole thread, it’s just amazing.