Simply let us know. Often a particular size is on back-order or en route to one of our stores or warehouse. When we receive an item that has been placed on back-order, we will reach out to everyone on that waiting list.
If the item is in high demand, we try to manage that demand and order more from the manufacturer when possible.
Then it is up to those notified to place their orders while supplies last.
So being on our "waiting list" is a great way to purchase a "hot item" and secure it when it becomes available.