You can also buy them online and at the Disney Stores before you go.
If you are already in Orlando, there are Disney Stores at Ocoee Mall on rt 50 and Florida Mall off of I-4.
Once you buy them, you will just have to have them activated when you arrive at the parks at Guest Services.
The drawback with getting them at the airports is they are already activated, which means if you don't use them right away, you have lost days.