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