We would like to experiment with installing/updating some tools on our ubuntu 12.04 LTS based appliance but Synaptic fails while reloading the package information with an error in it being unable to find the repository.

We understand that 12.04 LTS is a really old version of Ubuntu.

However, upgrading ubuntu is neither required for our needs, nor practical given the deployment of the appliances around the world and many other practical considerations. It appears that the repository has been moved in the past few months as we had been able to reload package information in Synaptic before that.
Where do I find the repository so that I can update a tool (e.g. tzdata).

Thank you.

Lu