There are some people on Ebay who are selling copies of pinball posters. the quick way to spot these are the sizes of the poster. Two that I have seen month after month are Safe Cracker and Monster Bash. 16 by 24 inches is not the right size. Here are the correct sizes.
Safe Cracker Rare Pinball Promo Poster 22 by 28 inches.
Monster Bash pinball Machine 36 inches by 24 inches.

Please check out my Pinball Guide listing all the pinball posters known with sizes.