I have hit the limit of how many computers my domain admins will allow me to add to the Active Directory. Most of these are old VMs which are no longer in use. How do I query AD to find a list of all the machines I have added in the past so I can go about removing some of them?
You can not. AD does not record who registered a computer in it. This information is just not available. Reorganize your processes to track this as part of the adding workflow.
Ask your domain admins to allow you specifically to add computers to a named OU; this lifts the default quota of 10 computers that all users may add to AD without specific administrator rights.