They REstock, but they do NOT change types of skillbooks - meaning that you can buy more of the same book over time, but you will not get new books until you reach some level (I think that vendors started offering more books since lvl7 or so).
Also, rain of blood isn´t necromancy spell. Its crafted spell, made from any water skillbook+any blood skillbook.
do you know where can i get blood skillbook?
