Unfortunately, the answer is: you don't.
According to previous responses, the cels were 
never made available, hence the severe shortage 
for us fans. In the three years or so that I've 
been collecting cels I've come across very few.
I have one of Dee and one of Ryo and I don't 
hold out much hope for getting any more.
Since the manga got translated and a whole load 
more fans appeared, the competition is likely to 
be even higher for any cels that DO appear for 
sale.
Sorry to be the bearer of bad tidings so here's 
my cel of Dee to cheer you up (thanks again Ms 
Poe)! You can see my Ryo cel at my site.
~Swordy