Hi June!
Congratulations on signing up for your first
runDisney event! I just know you're going to have a great weekend.
The runDisney New Balance shoes are so cute. When new designs come out for races, they are definitely popular items. New Balance learned from their first few runDisney events, when the lines were ridiculously long, that they needed a system. During race weekends, they now offer an "online queue" where you can sign up and get a window of time to come and shop. The quicker you sign up in the queue, the earlier your shopping time will be. New Balance also learned to bring a much bigger stock of shoes to the expo.
IF there are new shoe designs for
Princess Half Marathon weekend (there may or may not be), you will get information about signing up for the queue about a week or so before the race. Generally, the shoes have not been selling out too quickly. I wear a popular size for women and have been able to get my size on the very last day of the expo at my last two races. It's a good idea to follow runDisney on Facebook and Twitter as they generally post information about all of this on their social media channels.
I hope this helps! Please let me know if you have any other questions.