Plus Size Halloween Costume?

I live in St Louis Missouri and want to know if anyone has an idea of stores where I can buy I plus sized costume around here? I don't want anything with a super short skirt, too tight, over revealing, etc but that seems to be the only kind of costumes for females....I am size 18 and have had children. I don't exactly feel the most comfortable in that kind of stuff. It's been years since I've worn a Halloween costume but this year my boyfriend and I are going to a costume party so I need to find one!