Sometimes packages are replaced with later versions and the old versions are removed from the Repository lists, but you may be be able to get access to the old .deb packages for manual installation (as long as they are current for previous Ubuntu releases).
This location has all the available packages:
http://archive.ubuntu.com/ubuntu/pool/main/
Just download the particular version for your system architecture and install (you may have to manually remove the current package version - and then "Pin" it so you are not prompted to have it updated).
I used it to obtain the "old" version of Pan (newsreader software), as only the new beta version appears in the repository list for 8.04.