Error: package has no installation candidate [duplicate]
The package is available, and you can find it at http://packages.ubuntu.com/lucid/nautilus-open-terminal There might have been a recent update, and you may have to update your APT cache.
Run
sudo apt-get update
and then try to install again.
If all fail, you can get the .deb package for AMD64 from the same URL above and install manually. You can install manually if you double-click on the downloaded .deb file.