Bob,
The posters were very popular a few years back but as all things of that nature they stopped being a big seller and were passed on down to smaller retailers. My guess is that if you want find a poster of that type that you try a head shop or try a local bookseller. I do know that when this item was popular there was a book published that had page after page of these illusions to peruse. There actually is a particular name for this type of illusion. I will see if I can find out what it is called and post it here. I think it might actually help if a person could get a hold of one of these posters and practice with it in order to develop the vision needed to see the blip page.
