My first comment would be to work out what sort of management.
i.e- are you looking to relief manage the smaller properties that really rely on their managers to be hands on in everyday such as making beds and laundry, or higher end where your management is more controlling staff who perform these duties.
When you have worked this one out, start with approaching a small pool within your desired area, ensuring that you do not have a situation where you are never available when needed.
Our relief guys may only look after 8 to 10 properties, but can almost stay in full-time employment as we like the others commit 6-12 months ahead for holidays.