The harlequin_sga comm. It grew from the sga_flashfic comm. They had the harlequin challenge (http://community.livejournal.com/sga_flashfic/tag/harlequin+challenge) and such was the love for the fic that some folk went and created a comm. Just had a quick look and it's not that active, but there is still life.

ETA: This post (http://community.livejournal.com/sga_flashfic/176558.html) in sga_flashfic talks about an archive: Stargate Atlantis: A Night of Harlequin Romance (http://www.eternalvox.net/~harlequin) but I'm not entirely sure what's happening with it, whether I'm missing something, or it never quite got started.