The grand parade is April 21 this year. I missed it last year, so I'm hoping to go back this year! I also haven't been in the parade itself in ages, just performing at the talent show instead, so that might be nice for 2013.
You can sign up for the anime costume section & contest of the parade at Japan Video at San Francisco's Japantown, though I don't know if they've started taking entrants yet or not! Anyone know?
Website for the festival is here: http://www.nccbf.org/