brendan cordina found his granddad 's wwii medals at a nt museum .
he spent two years looking for jack slade 's medal 's believing they were lost forever .
a request to have them returned to the family was refused .
mr cordina was told that the museum needed them more than he did .
he has now started a petition to have them returned with 15,000 signatures .
director of the museum said mr slade asked for them to be left to the public in his will .