The posters are in the following places...
1.In a young boys room in the sector 5 slums, the house it the most eastern i the small village, and the power is upstairs in his room.
2. the back of the Ground floor lobby of the Shinra Headquarters in Midigar.
3.Next to item shop in the ghost hotel of the gold saucer.
4.Next to weapon shop at cosmo canyon.
5.In the inn, at cosmo canyon.
6.And finally, in Yuffies basement of her house in Wutai.