The most recent source code for KiCad can be downloaded from the GitLab repository.
See the developer documentation site for instructions on how to build KiCad from source. You may also want to look at one of the existing packaging repositories to see how KiCad is built and packaged for our officially-supported platforms.
If you are interested in packaging KiCad for a new platform, please contact the KiCad core team via the developers mailing list to let us know about your efforts and so that we can provide guidance and support.