I already got Blaziken and Sceptile, but I want to know the rates for finding these starters so I know what to expect.

They seem just as common as any other Pokémon. That being said, they are rather common. commented Nov 6 by PrimalKyogre

It appears that they have the same chance of appearing as any other Pokemon. There are 226 different Pokemon that can be found in Dynamax Adventures and 6 of them are Hoenn Starters. (Grovyle, Sceptile, Marshtomp, Swampert, Combusken, and Blaziken.) Therefore the odds are 6/226 or 3/113. That leaves you with a 2.66% chance of any random Pokemon in a raid den happening to be a Hoenn Starter

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