For Ubuntu and related distros, there's a daily builds PPA, which provides frequent updates of changes, bug fixes and additions.
# add daily builds PPA
sudo add-apt-repository -u ppa:snwh/ppa
# install icon theme
sudo apt install paper-icon-theme
You may download the latest version of Paper directly as a Debian archive.
Paper Icons# install the deb
sudo dpkg -i paper*.deb
# install dependencies
sudo apt install -f
For RPM-based distributions, repositories for Paper and instructions for adding said repositories to both Fedora and openSUSE are available on the openSUSE build system.
Paper IconsSome lovely folks in the Arch community are maintaining Arch User Repository package(s) that provide both the Paper icons and GTK theme.
Paper Icons