ServletContext is an object, which is passed to Servlets by the Servlet Container. So source is servlets. I think you can try following ways.
You can pass servlet reference to the Class which is going to use ServletConext. Once servlet reference has come you get ServletContext also.
Another way is to implement ServletContextListener interface by this class. Whenever ServletContext is created this class will get notification and from the event ServletContextEvent you can get ServletContext.
Actual scenario is not clear to me, so I am just throwing ideas. But I think above ideas should be able to help you.