Install it from your OS distribution (others coming soon)
# yum install virt-manager (Fedora)
# apt-get install virt-manager (Debian)
# emerge virt-manager (Gentoo)
# pkg_add virt-manager (OpenBSD)
Or grab the source release
The code is browsable online.
Get a personal checkout from GIT
# git clone \
https://github.com/virt-manager/virt-manager.git