This is binaries-only.

Is the WordStar source code out there?

It seems not, but there is an open source clone called WordTsar with source included:

https://sourceforge.net/projects/wordtsar/files/

I migrated the project to GitHub with extracted sources, so now it's browsable online:

https://github.com/sleaze/WordTsar

Latest source: https://github.com/sleaze/WordTsar/tree/master/Releases/Word...

What was wrong with all the source (including branches, etc), being on Sourceforge?

You can't see or browse the source without downloading and extracting zip files.

After clicking around more it looks like there is a mercurial repo you can browse.

https://sourceforge.net/p/wordtsar/mercurial/ci/default/tree...

Have you uploaded a copy to the Internet Archive yet?

Looks like development is still active, I missed the "mercurial" button earlier, oops.

https://sourceforge.net/p/wordtsar/mercurial/ci/default/tree...