I tired to contact former Polish translators but without luck so far.
For
mail.mozilla.org we needed Polish templates in unicode, so we created
https://github.com/aviarypl/mailman-l10n-pl repository and it now contains message and template files converted to UTF-8, corrections and additional translations. I'm also planing to keep it updated for 2.1 branch (right now 2.1.19rc3).