DC event listing sites of a general nature:

• Gregslistdc.com
• Culturecapital.com
• Washington.org/calendar
• Eventful.com/washingtondc/events
• Washington.dc.eventguide.com
• Prosinthecity.com
• Diningindc.net/
• DCyoungpro.com

Or you could always create your own event – on a boat – as in this video for Odyssey cruises (not an ad – just like to be on boats like this sometimes):

Add more sites in the comments if you know of them.