You can get it from http://search.cpan.org/dist/perl-5.12.0/ .
The official release announcement is at
Perl 5.12.0 represents approximately two years of development since
version 5.10.0 and contains over 750,000 lines of changes across over
3,000 files from over 200 authors and committers.
This is the first major release of Perl following both the change to releasing
on a pre-planned regular schedule rather than on an ad-hoc schedule, which is a
vast improvement for timely access to the latest improvements in a simple and
stable manner. This is also the first major release following the switch to
using GIT as the version control system for Perl 5.
See the release announcement (url given above) for more information, including
what some notable changes are, details on the release schedule, and credits.
Perl 5.12.0 should be quite solid, but please make sure to test it with your
code bases as soon as possible if you like to stay up to date, so any possible
issues can be addressed sooner rather than later.
-- Darren Duncan