Where can I purchase (for home use) a metal cylinder (preferably
aluminum/ steel) approximately 15" in diameter and 9" tall? I want
something that's fairly light, open on one end (like a trash can), but
durable enough that it won't bend. I'd prefer it if it were not
curved/ beveled on the edges (like a cooking pot.)
Essentially, I'm looking for a very simple trash-can shaped container
(which has no decals/ markings on the exterior.)

many machine shops will make single custom items like that, but it
might cost you a few hundred, it might be worth it to call a few and
get a quote.

Maybe try http://www.mcmaster.com  they have many items as well as metal stock.