Get Last Login Time of Organization Admin

I have been using the Organization API, particularly, the audit log of events endpoint, to gather login data of our users. One user that does not show up in the audit is the administrator account. This is probably because the associated email address is not part of the domain.

Is there any other way I can obtain the login data of an account not associated with the verified org domain? If not, is there any way the associated email address for this admin account can be notified when their account is logged into?

Thanks in advance!