Here are some alternative move options for Volcarona (and I'm putting Hidden Power at the end):
Giga Drain: Giga Drain's synergy with Volcarona is obvious, as it hits the Water and Rock types that Volcarona's Fire moves would be not very effective against. Throughout the generations, Volcarona has used Giga Drain to throttle supposed checks, such as Gastrodon, Rotom-Wash, Slowbro, and more Water types in Generation 5 and 6 all the way to Tapu Fini and Urshifu-Rapid in Generation 8.
Psychic: Psychic is another great coverage move, mostly to deal with a few Pokemon that Giga Drain can't handle. Most notably, in Generation 5, Tentacruel is hit quite hard by Psychic while Keldeo can be outright OHKOed after a Quiver Dance boost. In Generation 7, Toxapex and defensive Kommo-O take on basically every other move in Volcarona's arsenal except Psychic, which can be further boosted with Psychium Z; the same can be applied to Generation 8. Generation 6 notably doesn't see Psychic used as much due to Volcarona gaining much more value out of Giga Drain.
Hurricane: This is the most niche of it all because it really only has a niche in Generation 5 Rain teams. With Quiver Dance boosted Hurricane, Volcarona has a powerful coverage move that hits Keldeo along with decent netural coverage across the board. Volcarona can also help Rain teams deal with problematic Grass types that may take on the Water types that Rain teams like to stack. Of course, with Rain's decreased presence in later generations mostly thanks to it not being permanent anymore, Hurricane was never really used anymore in favor of the first two coverage moves.
Hidden Power: I know Hidden Power was explicitly stated to not be mentioned, but I figured that this can be useful to someone who would want to use Hidden Power. For Volcarona, Hidden Power Ground is 100% the best HP type. One Pokemon that stonewalls all of Volcarona's moves is Heatran, with Flash Fire covering for Fire. HP Ground smacks it really hard while also being able to hit Toxapex for solid damage. Hidden Power Ground is generally considered the best coverage move in certain metagames, like Generation 7 to hit Mega Charizard X, Toxapex, and Mega Diancie in one move; and in Generation 9 National Dex, for largely the same reasons. In basically all other metagames, Giga Drain is preferred for its utility against basically all Water types.
Since you stated you do not want Hidden Power, use Giga Drain. For any future players, consider both Hidden Power Ground and Giga Drain and base it off of what Pokemon and popular and what your team needs. Psychic is a viable option if a lot of Psychic-weak Pokemon are viable; Hurricane is a niche option and probably won't be used in modern generations, but maybe it can squeeze out a purpose.
