There are two possibilities:
- The item is actually a NEW item that we haven't sold before, but because we need to list it on our store and since our shopping cart software doesn't see any inventory on our shelves it will show as "Sold Out" - even though we may never have had any to begin with. Normally items like this will have a very clear availability/launch date window in the product listing page.
- The item just flat outsold a bunch of units and we ran out of them. Again on these items, we will normally put up some dates on the site when we expect to get them back in stock.
In both cases, if you want to be notified when we get more of them in stock or we are going to launch a new product for the first time, then you should click the blue "send an email when back in stock" button on the upper right of the product page you are interested in. That way whether we are doing a pre-sale or just putting items back into stock normally - you'll get a robo-mail from Shopify letting you know the item is available for purchase.
The "back in stock" button looks like this: