“By this logic there wouldn’t be gallon containers of Chalav Stam in stores. Yet we see many gallon containers of Chalav stam in stores.”
The strategy of a large retailer such as walmart or target is not the same as the local jewish store. certain products are considered loss leaders. Is why you sometimes see a gas station sell a gallon of milk out of their convenience store for $3.49. Heimishe stores also use this concept, but slightly differently. Before the 9 days for example stores may be selling things such as fish and pasta at lower prices to get you into the store. Some stores actually sell meat at a very low price during the 9 days to get you into the store. Unfortunately, for the chalav yisroel consumer, milk is usually not part of that strategy.