On the ShopStyle iOS app (download here) there is a "Follow Search" capability that will help you track items if they come back in stock!
Search for the specific item you have in mind (include, color, size, even price, if you'd like!) using the filters feature. Once you've narrowed down your search, tap the "+Follow" button. Even if there are no products there, you can still "Follow" this search and keep an eye on it on your home tab. When new items matching your filters come in stock, you'll see them immediately on your home tab!