Spoiler warning: Quest and/or game spoiling details follow.
50 of these are needed for the Assassin Outfits Quest.
50 of these are needed for the Barbarian Outfits Quest.
1 of these is needed for the Jester Outfits Quest.
Can be obtained by giving 150 Green Tunics to Irmana, which can be bought from Rudolph for a total of 3750 gp.
Spoiler ends here.