Is there anywhere in tokyo where I can buy old subway ads?

Question:

I want to buy used subway advertisements, also tokyo subway p.s.a.s. Does anyone know a place to do this?

Answer:

Yes, there are many interesting and beautiful ads in the trains. Many people want them for their collection. The train companies change them almost every week, so people may think that the ads may be available to the public once they are removed. But train companies, not only subways, would not sell them to anybody, saying (officially) that "these are not for sale, all the paper must be recycled for new ads to be printed next week." I guess they have a regulation among the train companies. If you steal them, you will get caught.