My best suggestion would be to keep a close eye on 
Ebay and Yahoo Japan.... Yahoo Japan is probably 
your best bet, honestly, for nicer cels... I'm 
still on the lookout for a better Keroberos cel, 
though admittedly I've been picky with 
prices/shots.  I got my Spinel through a trade 
with someone at Anime Expo a couple of years ago.
Also, probably general advise, watch updates of 
other cel sites... a few of them like AnimeGame 
have had some in the past.

Best of luck!