I think that Team Galactic's members usually have Dustox.
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You can find a dustox in eterna forest and there is also a trainer with dustox there too.
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
The trainer on Route 209 has Cleffa in Pokemon Platinum. Cleffa is a fairy type Pokemon and can evolve into Clefairy.