Unidentified Scroll

I already made the 'Cleverness' quest two times, and I botting on sewer area, killing Frogdrakes and GreenRats for like 3 hours, and still haven't get any scrolls.
Do you guys had any luck with them?


EDIT:Just got one, I guess that the drop rate is between 0.1% and 1%.

#actually never gotten a scrool