Any piece of cloth, leather, what ever will do the job of the bellows
strap, To attach use either contact cement or rubber glue and follow
the instructions. The D-ring get from a hardware shop or even a
locksmith shop.

Good luck,

Draco

Getting even isn't good enough.

Being better does.

Bellows is more likely to sag when using a long bellows
draw, Calumet actually made three(?) different Orbit models
with different monorail and bellow lengths, you can probably
pick up a used orbit for less that a replacement bellows for
the "system" cameras, for occasional use I would just prop
up the bellows from below after I set the shot up.
darkroommike

    I replaced the bellows on my Calumet C-1 some years ago
with a new one bought from Calumet. It came with one bellows
strap in the form of the same cloth the outer bellows
covering was made of. I used the old D ring. The strap had
some sort of adhesive on it. The same for the replacement
bellows I got for my ancient Agfa 8x10, the strap was just a
strip of cloth. A good place to try for the ring is a tack
shop, i.e., a place that sells stuff for horses. Also, try
Tandy Leather, they have all sorts of rings and buckles.
    The straps are used either to pull the bellows up if
they sag or, if you are using a long bellows draw, run a rod
of some sort through the ring and let it sit on the top of
the camera frames.
    Probaby the best stuff to stick the strap itself
together with and to mount it is contact cement like
Pliobond or Barge Cement.