If you're lucky enough to live near a dance shoe store, or a studio that carries an inventory of shoes, check them out. It's always better to buy shoes in person so you can try them on, if you don't know your size (dance shoes are different from street shoes). Competitions also often have vendor stalls, where shoes, jewelry, and other dance attire is sold. However, if this is your first pair, you will probably want them before the competition. If you have no other options, you'll have to order them online.