This is a tool that mirrors original upstream distribution files in OPAM
packages. It places them into a distfiles/ directory that follows a similar
structure to the existing archives/ directory.
Assuming that you have an OPAM checkout in ~/git/opam-repository, do:
opam mirror-show-urls ~/git/opam-repository > package-list
opam mirror-fetch-urls package-list
or
opam mirror-fetch-urls - | opam mirror-show-urls ~git/opam-repository