How to find available registration keys for a parent organization?

Please go to  License Portal → License management → Overview → Select master organization → Input keyword "LIC-SRV-Registration" in Entitlement filter → Find the lines in the "remaining" column that are not blank. 
 Example : Under master organization  Advantest_Training  sub-organizations  Advantest Training 2  and  Advantest Training  have available keys for registration.