Hello @ericrioux Are you using a default Magento feature? If yes, you can upgrade it by using this Out of Stock Notification extension. It will let your clients control their subscriptions as well as set alerts for out of stock options of configurable products as well as grouped products. You can control which items sold in your store have out-of-stock-notification feature. Alternatively, you can let your clients to pre order items, please have a look at the Pre Order extension. However, it may not suit you since, as you've mentioned, many of the product you are selling are restocked not very often.
... View more