Where can I get former bleeding-edge deb packages of Opera Browser?

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http://askubuntu.com – In a separate question I was looking for older versions of Opera that still have opera-unite. After finding that, now I use v11 (with opera-unite) and, in order to have access to the latest Opera, i have installed the bleeding-edge version (12.50 as I speak). I would prefer to act the other way around: to have the latest stable release and even to add it to repositories, and get updates etc, and use a separate version of v11 (for opera-unity), that I would suspect could be a former alpha/beta/nightly build from a previous stage. Where to find that? In Ubuntu (and in Windows too) one cannot (HowTos)