You have two carrier cards from the beginning..missile and area effect..you can buy few more if you wish..but you will gets lots of carrier cards and blank spell amulets when you progress through the game!!
It is worth noting that necromancy is essentially forbidden, legit merchants shouldnt sell you these spells.
In the first game, you had to talk to slightly hidden shady dealers just outside of town, they had ''forbidden wares'' to offer.
So dont be shy to post random info about where you find these dealers or cards...as necromancy is most likely the most difficult mage path to take. (in terms of progression, im sure it is quite powerful)