So far there is no ebuild for rzip in portage. Reproducible: Always Steps to Reproduce: I made my first ebuild, it's very basic, but it works for me.
Created attachment 29072 [details] ebuild - first attempt
Hint: you can remove src_unpack and src_compile, they do that stuff by default. Also dodoc COPYING
added to portage, you'll help me maintain this, though