I finally found and added re-stock notifications for out of stock items!
When you are on the page of a sold out item or variant, it will allow you to sign up for an email when the item returns. This form is only used for restocks and not my email subscription list. I've included a photo of what the form looks like. You'll enter your email address under the faded-out 'sold out' button where 'add to cart' would normally be.
If the form does not show up under an item that is marked as out of stock, it likely means that the item will not be returning any time soon, if at all.
This is a new app for my site, so please let me know if you have any feedback, questions or concerns regarding it! You can email me at: info @ lilboatboutique.com or hit the "contact" link at the bottom of the page.