On Wed, 26 Sep 2018 14:02:37 -0000 (UTC), NotReal , in
Did you update the package list?
sudo apt-get update
Once you do that, then you can do the apt-get source sunclock and get something like this:
Reading package lists... Done Building dependency tree Reading state information... Done Need to get 1,585 kB of source archives. Get:1
Then you should see 13 patches being applied, and ending up with a directory called sunclock-3.57. From there, you can make your changes, then build your own .deb package, and then "sudo dpkg -i sunclock(stuff).deb" and install in the usual way.
That's because some of those source packages will generate many binary packages. For instance, the source package gcc-8 generates 190 binary packages.
Take a look: