Think of any "big data" company -- but moreso - think of anyone who is using Amazon Redshift for BI...
But really any company who can say they have "a data pipeline" will be a good candidate.
If you have very deep Postgres knowledge, then make sure you have strong ability to ferry data in and out of the DB esp. on AWS.
There are so many people who are looking to move data into and out of Redshift, RDS or other standalone systems. Any company who uses the term ETL will
Also - there will be a good number of people who want to migrate, at least in testing, from Postgres to Aurora (mysql based - but instance-less) -- so this will be a good skill.
I've primarily been a Postgres DBA for the last decade or so, and have never had trouble finding work. As Postgres grows in popularity, people who know what they're doing with it are in increasing demand.
Edit: I'm thinking of more DBA type work and assisting with/contributing to drivers/wrappers.