Here is everything as a torrent:
http://bakabt.me/128719-yu-gi-oh-osts.html [320 kBits]
FLAC is very hard to find. There are a couple of torrents out from 2007 but they're all dead. However! the group who originally released them is none less than LosslessONE! In their IRC channel you can download this package: [LonE]_Various_Artists_-_Yu-Gi-Oh_Duel_Monsters_Duel_Vocal_Best!!_(FLAC).rar which is really nice. :)
Here are two other file names which I could not find anywhere, just dead torrents. :/
[LonE]_Various_Artists_-_Yu-Gi-Oh_Duel_Monsters_-_Sound_Duel_1_(FLAC).rar
[LonE]_Various_Artists_-_Yu-Gi-Oh_Duel_Monsters_-_Sound_Duel_2_(FLAC).rar