Finding genuine stuff from that early may be difficult. Even the Mabinogion is a later collection of tales (assembled around 14th C) You could approach Trinity College and see if they have anything in and around the Kells or Durrow era but I believe they are mostly religious works preserved from pre 10th C.

Otherwise as suggested Early welsh and Irish story collections Mabinogion, ChuCullain, Romaunt de la Rose, and Chaucer are about as early as you can go.

Good luck to Ms Zettels project. I thought her book "The Fools War" was excellent.