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