lol i'm the same a carmilla
i found my Yamato orochi on a floating fortess floor in WWC 30+floor though...
i've checked a few faqs... i got this that says you can find it on a water floor O.o

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/ FLARE GIGAS /
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HP: 1050
EXP: 2000
GIL: 2000
WKN: None
LOC: Water Floors (!); Cavern Floors; Fire Floors

a very good source that helped me out with every other one (i forget her name... she's from this site though :P) tells me i can find it on the lava floors in WWC...
after i check the water spring temple again... i'll have to go back to WWC and hope for the best T_T

(i'm aware the last post to this thread was made a year ago and i'm probably typing to the screen :P)