For those who are wondering about the best place to farm them, I recommend going to the first room of the 2B floor in Emil's mansion. Once you open the door to the second half of the room about 5 waves of the small shades spawn with like 10 shades per wave. Activate Dark Whirlwind with 2 blades before opening the door and see them drop items left and right. I got all the metal bats I required for upgrading the metal pipe in no time.
Once you kill all the little shades just go back up the stairs and return down and they will all respawn. It's a much quicker method than chasing the small buggers in the north plains or going through the fortune teller's "dream" over and over again.
'Sonny, what's the name of that nasty German who keeps hiding my stuff from me?' 'Alzheimer, grandpa.'