How to get Koseki tohon and sansei visa if my father is not willing to provide his documents?

I’m a sansei and my father is Japanese descendant born in Brazil. Only my grandparents (from my father’s side) are Japanese. Problem is that he is not willing to provide the necessary documents for me to get rhe Koseki and the sansei visa.
What can I do in this case? I have no family living in Japan.

Thanks

by Choice-East-9702