ScreenBear, I gave this response in the "tripe sandwich" forum in response to your question there. Maybe you missed it:

"The section of Paris I believe was Les Halles, but that has been cleaned up for a while…in general, while in France, look for restaurants that are close to or contain in their names the term "les abbatoires" (slaughterhouses, or stockyards, to translate roughly). Inevitably, the specialities will be all sorts of wonderfully prepared organ meats: tripe, kidneys, liver, sweetbreads, etc."