There are a few ways of getting Dragon Coverage in Gen 3, but very few of them are good.
You could try and find something with a Dragon Hidden Power, but that’s RNG based and requires a lot of testing, resetting, and a Hidden Power TM.
Outrage Existed in Gen 3, but there are hardly any non-Dragon options, only the Charizard and Tyranitar line learns them in any capacity. And both are weak to Kingdra’s Water typing.
Dragon Claw is also a potential Super Effective move, which can be learned by TM which is available from Meteor Falls in Gen 3. Non-Dragon Pokémon that can learn Dragon Claw in Gen 3 are Aerodactyl, Aggron, Charizard Line, Feraligatr Line, Groudon, Mew, Sceptile, and Tyranitar. Sceptile is the only plausible option that is not weak to Kingdra’s Water moves.
Dragon Breath is another option with Aerodactyl, Milotic Line, Steelix Line, Sceptile line, and Horsea/Seadra learning it, though most of these you’ll have to get it via an egg move which is less than ideal.
And finally, we have Twister. This is available for Gyarados, Milotic, Mantine, Pelliper Line, and Horsea/Seadra.
Honestly though, I think it’s easier to either bring your own Dragon Type anyways or settle for Nuetral damage. :P
Source, Source
Hope I helped!
