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