Centaurus,
Bear with this I know it sounds a little like Blue Peter:
I had exactly this problem and I solved it in a noval if not unusual way. Get a compass, little walkers type. Get a magnet and a map. place the magnet under an NDB shown on the map stick the compass on a cardboard cutout of a little aeroplane and hey presto you have an ADF simulator. The compass will always point at the magnet and you can demonstrate all sorts of scenarios.