I dind't really give it too much weight today when i found it, but i actually encountered a Soul speed III book in a ocean ruin (I'm playing on a 20w11a world, seed -2029173487062207931).
Sadly i did not take note of the coordinates so i techically have 0 proof but the knowledge i did found it, bui i'm guessing it can be checked in the loot tables. 77.72.32.212 21:24, 17 March 2020 (UTC)Rio_Thunder