If there is no one willing or suitable to be a decision-making representative known to the applicant or the Relevant Person, the Court can appoint a decision-making representative from an expert panel maintained by the Decision Support Service.
The application process and the required documents are the same as outlined for Capacity Applications (see How do I make a Capacity Application?). You will indicate on page 6 of Form 55A that you do not know of a suitable person who is willing to act as decision-making representative for the Relevant Person.