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