There is a new flag under Settings that will help find clients without any patient attached.
Go to System - Settings

Then to Global - Choices - Find empty clients in metasearch

When searching for clients without patients attached go to Names - Clients/patients - Edit, search for "0" and the list will appear in the metasearch.

It's possible to edit the client and add a patient by doubleclicking on the specific client, press Create and then add a patient that way.