[snip]
This question was asked often enough to cause the existence of
https://www.debian.org/CD/faq/#not-all-images
which says
"We don't store/serve the full set of ISO images for all
architectures, to reduce the amount of space taken up on the mirrors.
You can use the jigdo tool to recreate the missing ISO images
instead."
The advantage of Jigdo for the DVD mirror servers is that the bulk
of data can be fetched from Debian servers which provide packages.
Jigdo loads a compressed ISO image with lots of holes and then loads
all the package files which fit exactly into the holes.