you can get a lightning spear, in Sins Fortress. you go to the area where you first see the giant boulders that hit the snakeman. head up there go thru the fog door. keep going till you get to the doorway where the boulders, are heading down and follow it down. go to the left and there is a room with a chest. this is a mimic. kill the mimic and you are rewarded with the lightening spear. level it up to +5 and it is yours.
To upgrade this to a + 5 you will need :
Lightning Spear + 1 = 1 Titanite Chunk
Lightning Spear + 2 = 1 Titanite Chunk
Lightning Spear + 3 = 2 Titanite Chunk
Lightning Spear + 4 = 3 Titanite Chunk
Lightning Spear + 5 = 1 Titanite Slab