It is rumoured that Rheinland battleships and cruisers like to eat Sunslayer torpedoes, but I do not know if they prefer them for breakfast or for lunch.

As to where the Sunslayer torpedo launchers can be bought: there is only one such place and you visit it during the campaign. The name of that place is a spoiler, of course, and that is why you have to look for it in the Spoiler Forum where your question has been asked & answered gazillions of times.