It seems to still be available, luckily.
http://grauhirn.org/txp/ is the author’s page-o-textpattern-plugins; http://code.google.com/p/textpattern-plugins/wiki/GhoCommentsInvite is its page on Google Code.]]>
This site needs some sort of upload option for plugins. You can’t rely on people to host Textpattern plugins without jumping ship to Wordpress or whatever. This has to be the 10th or 11th plugin I’ve tried to download only to have the link bring up a 404 error or a “Welcome to your new Wordpress blog!” page.]]>
The links to download this plugin are all busted.]]>