User blog comment:Evil Grin/Going nuts MHP3rd! Cannot find Thn Anct Shrd!/@comment-2214216-20110227135257

I found out:

You can't get those shards from mining. You can only get them from the monyan wagon. For thin ancient shards, send them to the Dobolbelk or Royal Ludroth quest. For long ones, send them to the Narga or Jinouga quest.