Other answers point to https://code.launchpad.net/~ubuntu-core-dev/livecd-rootfs/+git/livecd-rootfs/+ref/ubuntu/master as the basis.
I cannot locate the scripts found at the links here: How are the Official Ubuntu Vagrant boxes built and published to Atlas? Following the links at the Vagrant related answer led me to a forbidden error here: https://code.launchpad.net/~cloudware/cloudware/+git/jenkins_kvm
livecd-rootfs
and compile – Rinzwind Aug 24 '22 at 20:10