An important thing to note about this quest is that Kirtida tells you the minimum requirement for this quest is only one mushroom, but if you bring more you will get a better reward. Go to the Golden Lair to find the mushrooms. The first mushroom can be found fairly close to the entrance on B1F. It will be in sector C4, in the second row, first square from the right. The quickest way to reach the second mushroom from there is to take the stairs behind the shortcut in B6. The mushroom is behind the molten scale in the top right corner of C6.