Need to find a wedding dress for a civil, backyard wedding while 20 weeks pregnant

Me

I already had a destination wedding but now we are planning our legal wedding. We will do a gender reveal at the same bbq party. It will be a small gathering and I need a cute probably short dress (preferably white). Any ideas where to buy one? Online or in store? I live in Canada (Toronto to be more specific). I will be about 20 weeks pregnant at the time.

Thank you