Where can I get a high quality High School Graduation Hat & Gown and what colors?

I just graduated early from my high school and we are having a ceremony in August. What colors should I wear? I got expeled from a comprehensive high school and I'm was going to an alternative ed high school for expeled students. They do not have any mascots nor do they have school colors. My school colors from where I graduated from was Green and Gold/Yellow. I was wondering if I should just wear the colors from the school I got expeled from or just plain simple Black and Gold. Where can I buy this High school hat and gown at?