where is a good place to find a posster?

Answer 1

Since you're asking this in the astronomy & space section, I assume you mean someplace off-planet. There's a great novelty shop in the Alpha Doradus system that sells every kind of poster you can imagine, even some made here on Earth! :-)

Answer 2

You must ask a better question. First, do you mean a "poster", than, a poster of what? There is no such thing as a"posster"!