Notification when a certain amount of product is purchased

We would love to have a feature that allows an email or text notification to the admin when a certain number of a product is triggered. 

Our example - we want to change communication on our website when we reach 75 class spots purchased.  Right now that means someone has to keep an eye on Ontraport but it would be so nice to have an email or text alerting us when we get there.  Thank you!