Here are some of the sources to contact for those interested in purchasing these posters, note that a lot of them are NLA and if found, very expensive.

http://www.allposters.com/gallery.asp?aid=470111166&c=c&search=14287&DestType=12&Referrer%20=http://www.google.com/search?hl=en&source=hp&q=porsche+posters&rlz=1R2IBMA_enUS331&aq=f&oq=&aqi=g2g-&KWID=15065394&KEYWORD=Porsche+posters&SEM=lang%3D1%26c%3Dc%26search%3D14287%26AID%3D470111166%26KWID%3D15065394%26Keyword%3DPorsche%2Bposters

http://www.vpracing.com/

http://www.autotrend.com/porschelist.html

http://www.drivewerks.com/catalog/fun_stuff/DWKS_poster_porsche.htm