Actually, I think it's just a bad link. If you click on Groups under Community, you'll find the Group in question under Seller Groups, which I can view just fine on this ID.

They have the group thing in the US and I got an invite to a few after some comic purchases n' stuff.

Anyone can make one - public or private - but only members can post so it's not quite as "public" as the forums, and usually themed around something or other.

Wish AAM didn't snuff it. :_|