With this logic, you can deem cars and their advertisements to be haram, Computers, Restaurants, Air Conditioning and much more ... All of these things were never mentioned in Quran or Sunna ... Doesnt make them haram. Whats haram is us using it in the haram or to promote whats haram. The bases of all things is that they are halal except that which Allah has clearly forbidden in his Book and the Sunna. And those things that are debatable in islam, we should avoid, and if you see people doing any of the shubuhaat then u should advice them against it ... If they dont take your advice you should never force them to as there would be no clear evidence on its prohibition.
In general, things that started to exist after islam should all be halal except that which conflicts with the well established rulings of islam. In the case of fashion shows, if the show doesnt include any exposure of awra, sexual enticement, or haram music then it should be fine in general. Unless your telling me there is an explicit saheeh hadith that says fashions shows or anything similar to it is haram ^o):?