You could use homebrew to install libpq.
brew install libpq
This would give you psql, pg_dump and a whole bunch of other client utilities without installing Postgres.
Unfortunately since it provides some of the same utilities as are included in the full postgresql package, brew installs it "keg-only" which means it isn't in the PATH by default. Homebrew will spit out some information on how to add it to your PATH after installation. In my case it was this:
echo 'export PATH="/usr/local/opt/libpq/bin:$PATH"' >> ~/.zshrc
Alternatively, you can create symlinks for the utilities you need. E.g.:
ln -s /usr/local/Cellar/libpq/10.3/bin/psql /usr/local/bin/psql