It appears to exist in public repositories: http://www.ros.org/debbuild/hydro.html
Can you install other ros-packages, for instances, ros-hydro-ros? If not, have you actually gone through the installation tutorial and added the repository, gotten the keys? Have you run apt-get update?
Also, what Ubuntu distribution are you on -- does it support Hydro?
Originally posted by fergs with karma: 13902 on 2014-03-11
This answer was ACCEPTED on the original site
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Original comments
Comment by ratneshmadaan on 2014-03-12:
I am on 12.04. Yeah, been using Hydro. Yes, I followed the tutorial.
It seems they just updated it. Have a look : http://cram-system.org/installation
the page now says to build from source.
Comment by gaya on 2015-06-13:
On 14.04 you build from source, on 12.04 you use the Debian. It's not a problem with the repo, it's your ROS setup.