How do you know it's never been found?
How would someone know it's hers if they found it?
Billions of people have lived and died on this planet and have been buried and their grave site has never been found. Big deal.
It proves nothing.
Your sect’s teachings are reprehensible.
All that nonsense about Mary being assumed into Heaven is just that, nonsense. The whole nonsensical argument ignores a very simple truth. Jesus Christ gave John the responsibility of looking out for Mary. John was the last Apostle to die. John wrote several of the Books in the NT. John never mentions Mary having any special role, or authority. Also, John never mentions Mary being assumed into Heaven.
If anything extraordinary occurred with Mary, John would have written about it.