Koumori Dragon can be obtained in the "World Championship Edition 6" booster pack.
you would have to download a hack from the internet
"Baby Dragon" is in the booster pack "Dark Beginning 2".
Rainbow dragon is found in the card pack "Tactical Evolution."
Armed Dragon LV7 appears as a Super Rare card in the "Soul of the Duelist" booster pack in "Yu-Gi-Oh! 5D's World Championship 2010: Reverse of Arcadia".
It is not available in Yu-Gi-Oh! World Championship 2010: Reverse of Arcadia.
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He used it in early dueling kingdom episodes, so yeah he does have that card.
Power Tool Dragon can be obtained in the "Raging Battle" booster pack or as a reward from defeating Leo an undesignated number of times in a Duel.
Stardust Dragon can be obtained in "The Duelist Genesisi" booster pack, or as a gift from Yusei Fudo after defeating him an undesignated number of times in a Duel or a Turbo Duel.
You have to wait until you beat the game I'm afraid. But you could duel Power Tool Dragon instead if you can't. They have similar decks.
armed dragon lv 10-World Championship Edition 4 pack dark armed dragon-Phantom Darkness pack
You can't.