An archaeological object without provenance often does not belong in trade. In the overview Security for collectors this is a warning text. It does not say how to obtain such pieces.

What you do

You do not buy what has no provenance. You do not dig where you are not allowed to. If you inherited something and you are unsure, you ask the competent authority before you sell it, post it, or take it across a border. Until then you store it dry, shock-free, and documented, without "cleaning" it, until someone with expertise has said something about it. Cleaning can destroy the evidence an authority needs.

The folder

What you know for certain, and the gaps as gaps. Photos. The correspondence with the authority you asked, in the document cabinet.