I need 50 blueprint 3's in order for me to customize a sword that I've been trying to get my hands on, but idk who drops this item or where to find it.

I haven been looking for thous myself and today i found some, once you make it to the second disc, thers a old lady in the pub in athlum, she tells you to go see emma(or ....) and after you will do this quest then once its complete you unlock the second guild hall fo athulumm, in there some challanges give blueprint 3. So far i only got a few but thats the first i ever found.

you get them for doing the guild tasks in the secret guild in athlum
in total there are 3 different guilds
doing guild task for each of these will give you the three blueprints