you can sometimes find spawners for wraiths i nthe hollow hills, but the problems is how to kill them.
I don't know for sure if it'll work, but you could try quicksand and see if they sink into it.
If you just want to kill them for glowstone dust, give up. Go into a swamp and find a witch hut and get a witch soul shard, they drop glass bottles, sticks, GLOWSTONE, REDSTONE and i think if you kill them yourself u can get a potion as a rare drop.
If you cant find a witch hut, just overload a aura node with a certain aspect as flux and it'll spew one out