Try Riverside Indonesian Restaurant. They ain't exactly buffet style but ten course meals. Perhaps they do cater for buffets.
You can also try this indian vegetarian buffet restaurant at chinatown point basement. The good thing is, it's pay-as-you-wish. Sounds a foreign enough concept but the point is that you pay whatever you think they deserve for the food.
You might be thinking, won't they be making a loss? Well not so, for face-saving and embarrassment often makes one pay more than what they feel like giving!