Finding inactive clients

I'm trying to figure out how I can be notified when a client hasn't scheduled an appointment in a specified time frame (say six months). I know I can send out automated reminder emails from Acuity. But, I'd like to personalize each one. So, I'd prefer either being able to run a report in Acuity or to get a notification maybe from a CRM like Hubspot. 

Any ideas? 

Thanks!