General

Dual Blader skill books? no need for nx?

basically yesterday i bought slash storm 20 from the cash shop because atm im making use of the golden temple to train a little DB up a bit

but today, someone traded me in cpq and said "Need?", and proceeded to show me a Slash storm 20 mastery book (50% success rate), and i bought it from him for 5mil, as my friend is also making a DB, and i figured if it worked (Which it did =D) it saves her 2.9k in nx

so i was just wondering, can you find the other cash-shop skillbooks in 50% versions from monster/boss drops? like flying assaulter, bloody storm, mirror image, thorns, etc?

thanks in advance