Are you looking for a place that has a specific menu for Cinco de Mayo? It is more of an American holiday than a Mexican one, so you might be hard-pressed to find something.
Maybe give Frida a try? They take reservations and the food was good when I went there a year ago.
If you are specifically interested in trying Mexican festival food, you might also try some local restaurants around the Days of the Dead (Nov 1 and 2) or Christmastime. I personally haven't seen much (aside from pan de muerto, sugar skulls and rosca de reyes in shops and bakeries), but then I tend to avoid Mexican restaurants.