If an item you want to get your hands on is showing as out of stock, you can set up email alerts for any restock by simply entering your e-mail address on the product page (see below image). This will not subscribe you to any other marketing emails.

Where we have an estimated date for when an item will return to stock, this will also be presented on the product page for the item in question. 

When the item becomes available again, you'll then receive an email to say it's back in and available to purchase!