Drupal Commerce - Out of Stock, customer clicks to notify store owner to order more
There are two similar kind of sandbox module for this particular functionality. 

One was started by me - Commerce Stock Notify

Another by itamar - Commerce Stocklist. 

Both can be starting point for further development. As I left doing anything else for this as he started it before me, but my module do what you want except mail template which I was supposed to do later.

But now I think, I will spend some time on it &amp; try to release stable soon :)