@turquoise-- I agree that if you want halal gelatin, you should shop from a grocery selling halal products. Most Muslim majority countries only produce and sell halal gelatin. So if you visit an Arab, Pakistani or Turkish grocery store, you can find halal gelatin and other halal products easily.
I think the closest gelatin to halal gelatin at regular grocery stores is kosher gelatin. But I'm not sure if it's suitable for Muslims to eat kosher products.