Joyeuse is Obtained as a reward from defeating the Norman Conquest Legion and from the quest for clearing the Hundred Years' War campaign.
Joyeuse is 10 base attack power higher than Durandal. Being only half a level worth of attack power, most people ignore the Norman Conquest Legion in favor of either farming the more popular, due to ease of access, Heavenly Scourge Legion for Durandal or the Hundred Years' War Legion for Hauteclere.