I usually search for packages using apt-cache (e.g. apt-cache search 'flash player') or by using the search functionality on https://packages.ubuntu.com.
Now suppose I wish to search the package list of an old Ubuntu release such as Ubuntu 12.04 LTS Precise Pangolin. How can I do it? apt-cache search ... only searches the packages available for the version of Ubuntu I am using. https://packages.ubuntu.com only searches a few of the latest releases.
I suppose I could download the package list from http://archive.ubuntu.com/ubuntu/dists/precise/main/binary-amd64/, but what do I do with the package list to be able to search it? I prefer using something similar to apt-cache search ..., but I do not want to mess up my existing packages just because I want to search an old package list.
For online search I would recommend to use the https://repology.org service.
If we search for xbattle
as the package of interest
it will show the following:
So this package was last available in 12.04 LTS. If you click on the xbattle then you will be transferred to the launchpad project page.