Substituting tomatillos I have lately come across good recipes, which happen to require tomatillos. Sadly, I don't have a source for tomatillos. 

Is there some way to substitute them in recipes? Physalis berries? Underripe tomatoes? If tomatoes, then which kind? 

Will it be a result similar to the original recipe, something definitely different, but usable, or so different that it only works by accident?
i would think the flavor would be different, but they really are similar to small, underripe (green) tomatoes. i might be worth a shot to try those in a pinch, but canned is also a good option.