This sound effect can be found on the Network Sound Effects Library, which was made by Sound Ideas. It is included in LION - BIG ROARS, ANIMAL, CAT from the Hanna-Barbera Sound Effects Library. Even though it is labelled as a lion sound, the sound actually is that of an elephant. Links: https://soundeffects.fandom.com/wiki/Sound_Ideas,_Animals_-_Isolated_lion_roar_01#Audio_Samples