They're not torpedoes, they're torpedo casings. I'm sure the vitals were the parts that couldn't be replicated, not the casing and such vitals are removed to make room for the body (thus all a civilization might find is the casing). Making casings can probably be done easily. For all we know, people on Earth could be buried in "photon torpedo casings". They could be shooting coffins in battle! They just happened to load them with bomb components.