Where to Find and Catch Monferno
From Pokemon Go Wiki
Monferno are found and captured in Nest and Habitat locations.
Nests
Monferno Nests are locations that consistently spawn Monferno.
Habitats
Monferno Habitats are spawn locations where Monferno 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: