The second link you gave "plasma-widget-stdin" can be found by searching in the main launchpad site by searching by package name(I was able to find it that way). The 3rd link goes to the Ubuntu launchpad website, which only searches Ubuntu packages. I'm not sure how you ended up on the "official Ubuntu only site" but if you end up there in the future, look in the bottom left of the screen, you will see the Launchpad name and logo, it will get you to the main Launchpad website and you can search for unofficial packages there. To go there directly, the website is :
(Which I belive answers your original question, but please read on)
The ppa that you linked to appears to be no longer maintained, so I would use any packages from it with extreme caution.
If you do find a (active) ppa that contains it, you can download it by
- clicking the click just above the package list "view package details"
- clicking on the package name
- clicking on the .deb package that matches you architecture (i386 for 32bit or amd for 64bit)
I would do this with extreme caution as well, often (but not always) the other packages that are added to the ppa are dependencies of that package that you want to add and using the new package with older dependencies can be unpredictable at best;
It may fail to install at all with the error that
xx package is needed then you will have to go back to the ppa that you download the individual package from, download the package the was the dependency, try to install it, then go back again download the dependency for the dependency, then install the dependency for the dependency, then install the dependency, then install the package you wanted(this is known in the Linux world as "dependency hell" for obvious reasons, ppa are used to prevent this problem).