That's absolutely a subject worth thinking about. In the world of the fic, while Pokémon are generally to be treated as people with rights and agency, there is a pretty strong separation between the worlds of humans and Pokémon, established by the Agreement. This includes the thing about how wild Pokémon don't get prosecuted in the human legal system, and I'm inclined to think for the most part it's not expected that human systems for mental health, etc. treat Pokémon - I'm sure it happens, when particular Pokémon want to and particular therapists are willing to take them on, but in general Pokémon want to handle their own affairs. There are fanfics where Pokémon are fully integrated members of human society, but this one does not function that way; Pokémon have rights, and they're people, but humans have limited jurisdiction when it comes to Pokémon (and vice versa), and human society isn't expected to provide for them in the same way it's expected to provide for its own people. And humans are not allowed to interfere with Pokémon societies's rights to set and enforce their own laws and standards and worldviews for their own members. In the Scyther's view, being suicidal when you've broken the Code is right and appropriate; if humans systematically funneled suicidal Scyther into a human mental health system where they're taught to reject the Code and keep living, they'd be breaking the Agreement. (However, there's no provision that an individual Scyther can't seek out help from a human mental health system, or an individual human can't decide to try to help their Scyther with their depression.)
So there probably wouldn't be official mental health resources for Pokémon exactly. Trainers are probably cautioned to watch out for any signs that their Pokémon aren't quite stable and release them if they're not confident they can function and behave appropriately within human society. I don't expect most trainers would ever quite have to deal with this sort of thing, though; Mark, as the main character of a story, happens to end up with multiple Pokémon with major issues that come out in dramatic ways over the course of the story, but most Pokémon probably don't suffer from mental illness to a point that'd come up seriously with their trainer.
It would absolutely make sense for more characters, like gym leaders (as I brought up with Marge and how Scyther and Charmeleon have this fight in Mark's battle with her), to be watching out for this sort of thing and ready to help trainers dealing with Pokémon that have problems bigger than they could be expected to deal with. It'd be neat to talk more about this worldbuilding, too! Like, have Mark think about exactly what they do teach trainers about dealing with this sort of thing, discussion of the Agreement and its implications in general, etc.
COMMENTARY DONE