Depending on the size and shape of the desired ice chunks.... Hobby Lobby has some molds for making rock formations for train dioramas; who says you can't pour clear resin, or plaster into them and paint them appropriately for ice? If you were to use clear resin, I'd mix up a bit with some blue dye, then paint it onto various areas of the mold wall, let it set up, then pour the rest. That should give a fair rendition, might take an experiment or two though. You could do basically the same with plaster I think, by using latex paint dabbed here and there on the mold walls then pouring in the plaster. The wet plaster should mix and blend the paint a bit so it won't actually look "painted on". As I recall, the molds were pretty cheap too.
When once you have tasted flight, you will forever walk the earth with your eyes turned skyward. --Leonardo Da Vinci It's better to teach a child what you know than what you think.