Does anyone know where this blueprint drop? Plz tell.
How about a screenshot of the blueprint or weapon itself?
Generally they drop at the dungeon with the same level (or close enough) on VH..
It should definitely drop from the last dungeon on the city you are in, very hard difficulty.
But if you are trying to get a blueprint of something specific, you should prepare yourself for over 30 runs.
I recommend just buying the blueprint from marketplace, it shouldn't be that expensive.
Press "C" to open the shortcut and type the item's name and see if anyone is selling it at a correct price, it shouldn't go for more than 500k naturally.