Hi Charlie,
Authorization files for Enterprise are found on My Esri within your organization. If you have the proper permissions, you would log into My Esri, go to the Licensing tab, select View Authorizations and see the Authorization Numbers. If you are not currently associated with your Organization in My Esri, you can request access on My Esri and your organization administrator will grant access. If you have any questions, please also feel free to email service@esri.com and have your customer service representative assist.
Hope this helps,
Josh