Books of Hidden Bodies are pretty rare. If you’re a Person of Some Importance, you can make them in the Bazaar Sidestreets. You can also get them on a rare success hunting for caches on the A fine day in the Flit card, unlocked with Shadowy 81.
If you aren’t yet a PoSI, I suggest focusing on other stories and coming back to this one later—you’ll need a ship for this one.