A daily ISO of Debian testing or Ubuntu 24.04 (noble) beta from prior to the first week of April would be easiest, but those aren’t archived anywhere that I know of. It didn’t make it in to any stable releases of any Debian-based distros.
But even when you have a vulnerable system running sshd in a vulnerable configuration, you can’t fully demo the backdoor because it requires the attacker to authenticate with their private key (which has not been revealed).
But, if you just want to run it and observe the sshd slowness that caused the backdoor to be discovered, here are instructions for installing the vulnerable liblzma deb from snapshot.debian.org.