Where the samples are to be returned to the family of the deceased, the family can make contact either with  their funeral director or the cemetery/crematorium where the burial or cremation of the deceased occurred.  Usually the first point of contact would be the funeral director.

Most cemeteries and crematoriums will bury or cremate specimens, if the original service for the deceased took place at their establishment. 

In the event that the Coroner, after diligent attempts to do so, is unable to make contact with authorised persons able to act on behalf of the deceased, the Coroner may make arrangements to appropriately dispose of the sample.

ED:  this answer relates to the New South Wales situation and may not apply in other jurisdictions.