12.x Find unmanaged computers without NTP

We don't use NTP, and we won't, ever(due to a long history of it causing major headaches). So unamanaged detectors will not work.

So without NTP, how do I find unmanaged computers in 12.x? Please don't refer me to the "Client Deployment Wizard" it does no detection of any kind to see if a client is managed or not, I have thousands of clients and don't have time or patience to check each one manually.