I believe there was one last year and the year prior. Is anyone running it this year?
If an Evangelion gathering does not materialize for this year, Evangelion cospeeps are welcome at the Old School Cosplay Gathering on Friday evening - http://forums.fanime.com/index.php/topic,20867.0.html
The OSG is a pre-2001 gathering, so everything pre-Rebuild of Evangelion. However this still includes nearly every character of prominence I can think of since they almost all show up in the manga, which technically began in 1994, regardless of how long it took to conclude. Yes, Mari is fine, she's in the very last chapter of the manga so it's fine. :D