<p>I'm writing a Perl script and would like to use a n-ary tree data structure.</p>

<p>Is there a good implementation that is available as source code (rather than part of a Perl library) ?</p>

I don't really understand why you want it was "source" rather than as a perl library, but you can download the source for any CPAN module.
I haven't used it, but
Tree
looks to fill your requirements.