Good cels of Koharu Hotta are hard to find -- I 
don't have one, and I've passed up a few.  Really 
good Seira cels are also hard to find, although I 
have a couple (not for sale) as a result of long 
searching.

You should be able to find Nene and Izumi cels 
without a lot of problem, as they are not that 
uncommon.  Check out this link:

http://search.auctions.yahoo.co.jp/search?
sb=desc&desc=%a5%d7%a5%ea%a5%f3%a5%bb%a5%b9%a5%ca%
a5%a4%a5%f3&acc=jp&&f=0x12&at=true&alocale=0jp

And also visit this site, and check the P9 
inventory of the dealers there -- there's a few 
good ones of Izume and Nene.

http://www.cels.org/db/keep-track.pl?cat:1