For something like that I'd say pre-book for the best seats Julie.

You could try http://www.broadwaybox.com for discounted tickets. I'm not sure if they'd have Lion King tickets, sometimes the popular ones aren't on there, but take a look anyway. By using them we saved a lot for our broadway tickets - it's perfectly safe and you just collect your tickets at the theatre in NY.

Many people suggest the TKS booths in Times Sq and down near the seaport (don't know the exact location but I'm sure somone will - and this one is less busy) but you can only buy on the day and are not guaranteed to get decent seats, so not sure how that would fit into your plans.

Hope that helps.