If you're talking about a grocery store's prepared food section, my guess is that they've never down the nutritional analysis on the food they sell. So far as I know, it's not legally required and it's quite expensive, so most probably just skip it. You could ask at the counter if they have nutritional facts. If they don't, try to find a similar dish from a restaurant that has calories listed or from one of the calorie counting sites like Fitday or CalorieKing.
Edited to add: I was typing while Amanda posted and we said the same thing.