Installing packages from older repositories (natty/raring)

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http://ubuntuforums.org – In case this has been answered I apologize, could not find anything on it. Summary: System is 13.04 (raring). Have a private (PPA) repository that I want to add applications from. The repository only have dist folders for up to 11.04 (natty). I have added the repository as "deb http://.... natty main" but it still doesn't show up in list of available sources (have tried adding manually and as PPA/key). When running "sudo apt-update) I can see that it is getting a hit on the repository. Question: Is it possible to set raring to install apps from a repository and choose the app (Hardware)