Can I find Gigantamax Pokémon outside of Max Raid Battles?

Solution 1:

TLDR: The Pokemon you find in the wild do not get the Gigantimax form and move that they would get if you caught them in a Max Raid Battle.

Although I'm sure you have already found this, here is a list of all Pokemon that have a unique Gigantimax form/move: https://www.ign.com/wikis/pokemon-sword-shield/List_of_Every_Gigantamax_Pokemon#Gigantamax_Drednaw

I can confirm that Pokemon caught in the wild cannot get the unique Gigantimax move since when I Dynamax my Corviknight that I raised from a Rookidee, it does not get the unique form/move just the default flying Dynamax move.

The real issue with this is the terminology Gigantimax. All Pokemon can become giant and get moves based on the types of their existing moves but not all Pokemon get the unique Gigantimax form or move even if it is the same species as the ones that have the unique form/move. I find it strange that they use the same terminology but that may be a misunderstanding on my part.

Solution 2:

Not only can Gigantamax-capable Pokémon only be found in Max Raids (excluding events/gifts), but they can only be obtained from Max Raids where they are encountered in their Gigantamax form - a Corviknight caught from a Max Raid in its normal Dynamax form will never be capable of Gigantamaxing.

Serebii has a list of which Max Raid dens each Pokémon can spawn in. Using the Corviknight example again, you can see that it spawns in den 32, den 61, and den 89, but only the ones encountered in den 89 will be in their Gigantamax form, and only those will be capable of Gigantamaxing after you catch them.