TO TIAWD: Why is it so important to find a “reliable source” ? Nothing is going to change as far as Halacha or hashkafa is concerned, so why is it important to you?
Secondly proving or disproving something that may have existed hundreds of years ago is virtually impossible. The truth is that we will never be able to go to a court of law and provide evidence that would stand up there to prove or to disprove – until Eliyahu Hanavi comes and tells us.
Let us suppose that I can prove to you that the Sambatyon was part of the Volga in the area of the Caspian depression. Let us suppose that the phenomenon existed during the time of the Khazars and ended some time after they were conquered. The city of Astrakhan could probably be reached in 50 days from Aden on riding camels (80 miles/day). Suppose further that instead of a supernatural phenomenon, this was an irrigation method for creating a barrier that had the purpose of defending from marauding armies for the 6 days when the men were in the fields, but inviting an attack on Shabbos when the men were assembled at home. Then what ? What good would that do you?