> I would love to know where they are possibly!!
> How much do they roughly cost? 

  For the Inuyasha commerical, there's a very small 
amount of cels floating around, but each one costs at least
a few hundreds to over a thousand bucks.  I saw a decent
face shot costed around 800 bucks.
  Your best bet is to wait for the TV series which it is
coming out in the fall season.  The studio that responsibles
for producing it still using traditional cel production
instead of using computer.  So there should be cels 
available when the studio decides to release them to the
market.  And you don't have to fork out several hundred
bucks for the cels from the commerical.  The TV cels are
going to be a lot cheaper.