So far, I have only one photo of a bellows which can be used. Many of the exterior details which I would like to photograph are all black, making it extremely difficult to get any useful detail.
Note the wallpaper style panels. (The green leather has been lost to color balance problems, I fear.
However, I'll fill in with some descriptive text.
The bellows is a complex combination of (some or all of) leather, cardboard, cloth, paper and glue, mounted between two frames which receive and support the reedpans, and which are attached to the action box by long screws through the action box's edges.
The bellows frame has blocks secured (usually at the corners) to support the reedpan at the same level as the top edge of the bellows frame itself. This top edge, and the inner surface of the frame is lined with a white chamois-like leather to serve as an air seal. The same leather is used as a seal along the top edges of the partions, the cross-partitions, and the center doughnut.
Typically, the screws from the action box are threaded into inlaid brass plates, secured by two small countersunk wood screws. However, I have seen some cases where there was a slot in the sidewall of the frame, covered by the seal chamois, in which was placed loose a rectangular brass plate with just a single threaded hole. The thread does not correspond to any readily-available tap and die -- at least in this country (USA). The included angle of the threads is wider than the modern standard of 60 degrees. The closest I can come to a thread designation for the screws is something like 2-42 (that is a #2 screw by diameter, with 42 threads/inch, which is an extremely coarse thread for so small a screw.
For the moment, what follows will have to be speculation, because I have never taken the extreme step of soaking an old bellows apart to determine the actual dimensions and shapes of the parts.
The walls of the bellows are trapezoidal panels, usually made of display-grade cardboard. They are joined along the short and long sides with (rubberized) cloth hinges on the inside of the bellows.
There is a variable-dimension diamond-shaped hole between the adjacent sides of the bellows panels. The panels touch at the corners of the long end, but the corners of the short end leave a gap. This gap is filled by a soft, flexible leather patch, which is probably the most critical part of the instrument in terms of flex life of the instrument's bellows (as long as you don't drag the corners of the bellows over your knee while playing.) This has to be affixed to the panels with them fanned out as though the bellows somewhere near its maximum extension, to allow enough slack for proper bellows expansion. I suspect that it also needs to be given a pinch into just the right shape so it folds properly when the bellows is allowed to close.
There is a long leather strip which passes all the way around the long edges of all the panels on a single fold. In some cases there is a butterfly-shaped patch of leather which is glued over the outside of the two panels and the short side. However, this latter may in some cases be a strip of leather at the fold, and a trapezoidal patch of leather or paper on each panel to cover the edges of all the other pieces glued in place. On many of the older learner instruments, the leather was dyed green, and the paper trapezoids seems to have been stamped from an inexpensive wallpaper design of the day. Fancier instruments might have a design which accentuated the trapezoidal shape of the panel itself, and which were obviously designed for the purpose. More recent instruments typically had panels of the predominant color of the instrument, green in older ones, and black in more recent ones.
Now -- we wait for me to generate illustrations to (hopefully) clarify my text.