I am going to our hospital's annual charity ball next month. An actual, genuine ball, with the men in tuxes and the women in floor length ball gowns.

Where in the holy heck do I find a ball gown?

I need a plus-size-ish, since I am right on the edge of 18s again. But actual plus-sizes are usually too big for me. Help!! Any ideas?

I really want to try these dresses on, so a brick-and-mortar store suggestion would be the best for me. Thanks everyone!