You can obtain the keycheck value from the disk via a recovery media.
Then download the XML from the ePO the system was in via 'Export recovery information based on Disk Keycheck'.
The issue is that the object has been deleted by ePO because of the "Transfer System". Because of this, i can't select the ePO system in the system tree and perform that operation.
You can select a random system and then do a export based on the disk keycheck information.
If you reinstall ePO and restore the db on a virtual server (obviously not connected to live network) you should be able to export the key. Then some jiggerypokery to get the file off the virtual server
Systems must be transferred via pushing out the agent from new ePO server (NOT system transfer) which i'm sure you are aware of now