should come out back of the dash with a plastic holder which may be part of the bulb or it might have a push fit capless bulb in, if its the push fit type should be able to pull the glass bit out of the plastic holder your local motor factors or them robbing fu'ks halfords should keep them i think. If the bulbs part of the plastic holder again your factor or halfords may keep em failing that find a dead metro, maestro, montego and prbs some rovers in the scrapper 10-1 they'll have the same bulbs in since half of the switchs etc in discos came from a montego in the first place