I had a friend of mine who had undergone the same situation in which he had lost his KCET verification slip. So what he did to get it back was that he first made a phone call to kcet(the contact number can be found out from the brochure) and explained them all about him losing his verification slip. So, they asked him to visit their head office in Bangalore. When he visited the head office, he was asked his Cet number, application number and some more details, using which they found his application and took a new print out and gave it to him.