Well, I don't know about NX, but for mastery books, you can do the Silent Crusade & Tera Forest quests for two 30 books, and you can get 20 books from EVO (250 coins each; easy to get if you're leveling there). I think some other quests give mastery books, but I'm not sure.
3DS Friend Code: 0903-2770-3378. aka Snack. R.O.B is married. He plugs his Memory Stick into a USB port every night. ~wizaro1