Where do I get them? I've been going melee for a while and it would be nice to get another option. I heard someone in another thread mention a sorcery trainer but I don't know where that is. Unfortunately I accidentally killed the pyromancer guy in the barrel.

Head down to the the New Londo Ruins. There is a blacksmith near the elevator that sells Soul Arrows and the casting weapon.

You been to new londo ruins yet? Just take the path below the fireshrine and take the elevator down. From there, exit the building ruins you start in and follow the cliff to your right. You'll find some stairs and an npc that sells spells behind bars.

@Mars: There are a couple of NPCs that will sell you soul arrows, one of which is locked in a room in Undead Burg prior to the Capra demon boss and another I believe is found by taking the elevator past the Firekeeper to New Londo and talking to the person behind bars. If you start crossing the water in New Londo you've gone too far. I hope this helps.

How do I get to New Londo? Where is the "fireshrine"? Is that Firelink?

@SuperfluousMoniker: thanks