heal small wounds : you get that at the start of the game. heals an insignificant amount of health
stun: you learn that when you become Erevi's apprentice. lets you stun and capture creatures
chain lightning: you learn that as Erevi's apprentic. does moderate damage, can proc on multiple targets. your imp learns t when leveling
magic weapons: erevi teaches you that when she sends you to investigate a cult. conjures a magic sword that disappears at the start of the next day
wither: you find the spell in a crate in the cultists ruins. does mderatedamage on hit, disables enemy healing ad does damage over time
summon: taught by Erevi when you build a crib for her daughter. lets you transform into other creatures out of combat
night vision: you can use it when you drink a potion of vampiric blood. lets you see in the dark
awe: you gain it by having one point of vampiric blood. gives the target girl a week's worth of affection
flame : your imp learns it when leveling. decent damage agaiinst a single target
mesmerize: your imp learns it when leveling. enemies skip their turn till the spell wears off
there are also a few other spells but since those are available only for temporary companions,I didn't list them
Why the sad face? you upset I didn't list the spells? or are you suggesting my statement was inaccurate? I stand by it BTW, The OP asked
"WHERE do I
FIND more?", If you need to FIND a spell, Erevi is the answer.
Chain Lightning IMO is the only worthwhile Spell,
You don't FIND Heal, Flame or Mesmerize, they happen when you play the game.
NightVision isn't a spell it's a potion...
Stun & Summon are just a means to complete quests.
Awe is the only one that might count as an addendum to my answer since it's an effect you might "search" for.