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