Some things built on top of that:
https://manpages.debian.org/man/debsnap https://manpages.debian.org/man/debbisect https://wiki.debian.org/BisectDebian https://metasnap.debian.net/ https://reproduce.debian.net/
That said, a couple things to try though:
Email Dan Helfman <witten@torsion.org> and ask if they have a copy lying around in backups anywhere. They aren't a Debian member any more but incredibly are still posting to the Debian BTS occasionally, as upstream developer of borgmatic.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1056364#10 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1096005#10
Contact the Icculus folks, the CVS server mentioned in debian/copyright of the oldest version of openal on Debian snapshot points to the Icculus server. Won't get you the debian/ directory, but could possibly get you some sort of CVS access.
Not a blocker for what I'm working on, but more of an itch to track down the lost version.