Another approach that's a little more work on the class side
but simpler on the JSP side is to have the class create
Map's for the various Map-like getters, so that in the JSP,
you just write

  ${ org.getDepartmentMap()[deptName] }

There are lots of ways to simplify constructing such Maps.
One way is something like the Mapper utility class below. In
the constructor for your class with getDepartment(), put

  Map myDepartmentMap =  new Mapper(this) {
     public Object get(Object key) {
       return ((Organization) getObject()).getDepartment((String) key);
     }
   };

and add the method

  public Map getDepartmentMap() {
    return myDepartmentMap;
  }

You can do repeat this for any other Map-like methods you have,
e.g., getEmployee().

The version of Mapper below is quite short because it only
supports Map.get(), which is what you need for [] in JSP EL.
Any other operation throws an unsupported operation exception.
It would be easy to add support for put().

package utils;

import java.util.AbstractMap;
import java.util.Set;

public abstract class Mapper extends AbstractMap
{
 private Object myObject;

 public Mapper(Object obj) {
   myObject = obj;
 }

 public abstract Object get(Object key);

 public Object getObject() {
   return myObject;
 }

 public Set entrySet() {
   throw new UnsupportedOperationException();
 }
}