Short Answer: We don't always know!
Your best bet is to visit the product page here on our website, find the "Email Me When Available" form on the right side of the page, and enter your email into the box. This will make it so that you receive an email at the exact moment that your item is restocked to our online store.
(Note: If you saw an item at a convention, it is not automatically "in stock" on our online store. We're a small company, and sometimes have to take our online stock offline temporarily to go to Conventions around the world!)