I would look at having a central database (support or management type) that contains this type of information.

Example:

- Create a management database on the instance your SSRS is configured on.

- Create linked servers to each instance you need to manage

- Create a procedure that pulls in your data from each instance and writes to a local table within your management database

- Create a SQL Agent job that executes that procedure on a schedule based on when the report needs to be run

- Build your report based on the data in that management database, allowing you to keep up with one data source.