Where can I buy a shot glass in Tokyo?

Does anyone know where I can buy a shot glass in Tokyo? Is it even possible? I`ve looked everywhere, especially in tourist areas and I`ve been unable to find it. I`ve even tried describing it to my friends and they say that they`ve never seen or heard of something like that. Is it rare? It`s meant to be a souvenir for a friend who collects them.

Has anyone even seen one for sale in Tokyo? Please share.