Where to Find and Catch Volcanion
From Pokemon Go Wiki
Volcanion are found and captured in Nest and Habitat locations.
Nests
Volcanion Nests are locations that consistently spawn Volcanion.
Habitats
Volcanion Habitats are spawn locations where Volcanion is likely to be encountered, but not guaranteed the way a Nest is.
Additional Tips and Information
Best Nests
If you know a really good nest or any of the nests above is really good, list them here: