I'm using Kubuntu (Ubuntu with KDE) and have just helped a friend, a Linux newbie, transition his Lilypond approach on his Linux box. My sincere advice is to just download the software from the website and use that. The installation is super easy and even easier to upgrade (once you've installed it once you then know how to upgrade it). The distros are notoriously bad about keeping Lilypond up-to-date so you are much better off doing it yourself. If you want a more detailed explanation hit me up and I'll go into more detail. But seriously, it is a far better, easier, and less messy method of using Lilypond.
As for your question, I am unaware of any PPA for Lilypond. There is one serious gotcha with PPAs which is that when you upgrade your distribution to a new version I think most/many/all(?) of your custom PPAs get disabled requiring you to enable the ones you want to use. And there might be some weird incompatibilities introduced as well. And it requires the PPA maintainer to keep maintaining their repository which for a smaller program like Lilypond might not actually happen.
Oops, there I was, once again, extolling the virtues of installing it yourself. Sorry.
Dave