Was told costumes are required and it’s a Superhero/Villain theme… 
I’m in Zhongli, but could get to Taipei easily. Any recommendations for stores?
From Ximen exit 1 turn left and you’ll find a whole row of shops on Huazhong St. I don’t know about Zhongli.
Thanks, Hokwongwei. Gonna check out Ximending this weekend.