From Fallen London Wiki
under Perennial Peer Items, there is another option for "A Sapphire, Allegedly Imbued with a Minor Curse", namely the Oneiric Key, the Bohemian Renown 40 Item. Offers a +8 Shadowy, so it's better in that stat than both the machine and the expensive Rook-Crowned Oneiropompic Stave that is mentioned there. Obviously, if you want both Shadowy and Dreaded, then it offers no Dreaded, but otherwise it's more accessible than both imo and gives plenty of shadowy, so I feel like it should be mentioned there