What I am looking for is basically a mod that either flat out adds a vampire version of Sorrine Jurard. So that you can still get the crossbow quests.

Are there any mods that already do this? The weapon isnt enough for me to want to switch sides, yet I'd still like to do those quests.

couldn't you just console yourself an enhanced dwarven crossbow?
All of sorine's quests are generic radiant quests anyways.