Presently, the best way to separate costumes is by having a Costume entry for it. The Gallery feature doesn't appear to be functional at least not at the present time. We're sorry for the inconvenience - I think the reason it might not be there anymore is because having a costume listing and a gallery for the same costume may have been redundant.
2014 Conventions :
Katsucon (Washington, DC) - Megacon (FL) - Colossalcon (OH) - Anime Weekend Atlanta (GA)
Upcoming costumes : Princess Garnet (coronation gown) from FFIX, Edea Lee (various costmes) from Bravely Default, and more!