To make the biggest notification impact, you need to do one of two things;
Either post your announcement where the greatest 'footfall' is, or;
Send your announcement to each potentially interested individual.
For the first of these, I would hazard a guess that the IGKT web presence gets its greatest number of hits through this forum and in particular, this sub forum (Chit Chat). Logically then, post details of every meeting, webchat, whatever here in 'Chit Chat'. You will find that doing this allows those who attended, to add comments both before and after the meeting which can further help attract more attendees at future events. Also, feedback through this forum to the meeting organisers will help them improve the content or structure of future meetings. As this forum is 'Chit Chat' there is no reason why meetings and their discussion should not be posted here, and creating a new sub forum or webpage will not get the message over because the footfall is here in 'Chit Chat'.
For the second route, doubtless all events are already detailed in the KM. But a more focussed web based method is to use the list of email addresses for everyone registered to this forum and send a timely reminder to them by email. If you prompt your contributors ca 10 days before the event with a summary of what the event will cover, then it will save them missing the post if they have not been to the forum lately. Don't worry about annoying folks, if they don't want any more prompts, they will soon let you know and you can remove them from the mailing list.
finally, dare I suggest it? Put a Meetings section onto the Wiki and use the above two routes to direct folks to that section. This route, you can even have folks contribute content to the meeting for use at the meeting should the speakers chose to include it.