Source
The source code for validns is available under the 2-clause BSD license from github:
https://github.com/tobez/validns
Versioned tarball releases of the code can be found here
Packages of validns by Paul Wouters are available for Fedora, RHEL and Centos. Simply yum install validns
.
There is a FreeBSD port of validns by Hirohisa Yamaguchi, which can be installed, for example, by typing portmaster dns/validns
.
Packages for other platforms will hopefully follow shortly.