have you been to http://www.anime-taro.com?
as they have the largest hxh collection i can 
think of, but i must say SD hisoka is going to be 
impossible as he only appears twice for a split 
second in sd form (long shot end cels too), and 
if you ever find one, i'll trade my soul for it.

well, your sister must have been really generous, 
if you are willing to even find and buy these 
cels.

hisoka with his hair down is slightly less rare 
but rare nevertheless.

red-eyed pika you have a much better chance at.

kuroro is fairly pricey.  if you wanna decent one 
with his eyes open, you're looking at very least 
$350+.  i've only seen 1 or 2 REALLY nice ones, 
but they went for $700.

killua in his jumpsuit?  i'm not sure which 
outfit this is, but i don't know if you are 
referring to the ova's.

good luck!