you can find it in the survival area
Dustox.
Eterna forest
DUSTOX
You can find a dustox in eterna forest and there is also a trainer with dustox there too.
I think that Team Galactic's members usually have Dustox.
You are able to get Dustox by evolving Cascoon. Wurmple-Silcoon-Beautifly Wurmple-Cascoon-Dustox
I think it's Dustox
Dustox can be found in Eterna Forest. it can also be found by battling these two bug catchers
eterna forest 10%
Cascoon evolves into Dustox at level 10
Wurmple can go one of two ways, it can evolve into a Silcoon or a Cascoon. Silcoon evolve into Beautifly. On the other hand, Cascoon evolves into Dustox.
you can find dustox above the resort area in the grass