Custom contacts field in Case Management not loading

Summary:

I want to create a number of custom contact fields in Application Composer which will be used on the Case Management form. When I select the Case Object I am unable to see the case contact in the list. The only contact types that appear are Assignee Party Name, Primary Household Party Name and Primary Contact Party Name but when I test it in Visual Builder the list of contacts are blank.

I know Case has a 'Party Name' field as a standard attribute but it does appear in the options listed. is there any other way I can get the contact fields to generate the stored contact names?