I'm trying to demonstrate
openssh-server (7.2) DDOS exploit attack. When I did
apt-get update or when checked at ubuntu packages both show only the patched versions. I'm not sure where to find the original package?
You can download whatever version of OpenSSH you are interested in from the official website of the project. OpenSSH 7.2 can be found for example here:
You need to build it from the source, but it should not be a problem.