Event Pokémon are not necessary if you're after in-game rewards such as the Shiny Charm.
Some people give them away, for example on Twitch, they are pretty much always cloned though.
If you have an older game, Pokémon Bank and an AR (which are fairly cheap), you could try to generate the Wonder Card or key item so you can receive the event Pokémon normally, there should then be no difference between it and one you actually receive from an event. Instructions can be found online if you are interested in this method, or I can PM you further details.