I was looking at a King Arthur catalog, and noticed they have a product called Dairy Starter, and this is what it says about it."Make your own buttermilk, sour cream or soft cheese with our Canadian Dairy Starter. Simply stir starter into heated and cooled milk or light cream, and let rest at room temperature for 8 to 24 hours. Stir and enjoy. Each box contains starter for 6 quarts of sour cream, buttermilk or soft cheese."
Perhaps you could use it to make your own sour cream. You might have to use a little gelatin to thicken it to the consistency of commercial, but it might work for you. King Arthur is on line and the product is 6521 Dairy Starter.