No evidence... And Dreamstone is out. Where the hell would Belthasar get dreamstone when even Melchior only had one tiny rock to fix the Masamune.
The only reason he had the rock is because you went back in time to get him some. I always thought it was not a question of quantity, more of convenience. Melchior says something along the lines that long ago, Dreamstone was everywhere. I take that to mean there are Dreamstone mines, where the ore is waiting to be extracted.
Ayla also mentions that her stone is a symbol of power, more or less, to make her chief. If Dreamstone really is housed in some sort of mine, they would have to mine it out. That's a bit beyond the technology of Ayla's people, who just use wooden clubs. That piece was likely one that could be broken off very easilly, and because of its rarity, became a sort of heirloom for the chieftan.
As to the Epoch being made of Dreamstone, I have my doubts. Where would he get it? After 65,002,300 years, it's probably not accessible anymore if it even still exists.
