if i were you, i'd try to buy them in advance just to be safe! when my dad and i saw it a few years ago, we bought them as soon as we got to Downtown Disney which was a few days before we saw it...and we got 1st row. which, by the way, was really cool if you like the action right in front of you, but it was difficult to see some of the acts. my recommendation is to try to get a seat that's back a ways from the stage, and, of course, in the middle of the theater (if you get what i'm saying) cuz if you get the very first row, you'll be eye level with the stage. but back to your question....buy tickets either as soon as you get to Disney, or over the phone (which, i'm not sure if they do over the phone stuff) you should be able to get a seat, no problem! and they do advice you to get to the theater at least 30 min prior to show time.
i take it this will be your first time seeing La Nouba? if so, it's a magnificent show! definately my favorite Cirque production! have a great time seeing it! :wave: