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.