Unable to find package ros-hydro-pr2-mechanism-msgs

Im new to docker. I am trying to install moveit for ros-hydro in a ubuntu12.04 OS. I am getting the error

Unable to find package ros-hydro-pr2-mechanism-msgs

When I use the following command line

RUN rosdep install --from-paths src --ignore-src --rosdistro hydro -y

Is there a way to obtain these files or continue to run the script despite some dependencies of moveit is missing?