When you can't find it in the grocery store, make your own.
Bring 1 pound of tofu to a boil in 2 inches of water. Boil for 5 minutes. Drain water, then add a bunch of washed and chopped cilantro or parsley. Blend in food processor with the juice of half a lemon or lime. Walla - you have tofu sour cream. How easy is that??