Unfortuneately, Habs tickets are the hottest ticket in town - there is always a high demand, but especially now. You can try scalpers after the game starts if they have any inventory left, but they probabaly won't (due to the reason given above)
You could always go to Toronto or Philadelphia - ever disappointed Leaf and Flyer fans are probably giving tickets away to anyone who will take them - however the quality of hockey isn't very good in those cities (unless Montreal is the visiting team
)