It's not possible to sell those costumes to npc. (Can't be seen on the list while selling npc) Can we? So our kafra won't be full.
I can only sell Princess Ribbon Crown Costume (#21126). And some of them are empty lines on panel storage search too: Jakk Costume (#20919) Ear Witch Hat Costume (#21120), Princess Ribbon Crown Costume (#21126), Master Cat Costume (#21131).
I don't know about Slurp costume, the only one I don't have.