Checkout analytics within Marketing Cloud tracking to find data on all your historical sends. Take the opportuinity to target this audience with a speciality communication rewarding them for their dedication with a short thank you, event invite or discount code. Your eComm specialist can help with these four steps to target this audience through eComm.
Have an excel file of folks that you want to email? Your eComm specialist can create a Salesforce Campaign to capture your audience for you to distibute messages to.
Do you promote your events via a printed invitation or radio ad? Ask your eComm specialist to create a custom, short URL to make registering for events easy.