Lady Gregory compiled everything she could during the celtic revival , I feel like most of the sources were verbal recitals of poetry as you say.
Discussion
Yeah, I've only ever come across prose retellings but there are bits of poetry that survive in the Welsh tradition (Teliesin etc). I always assumed there would be plenty of Irish material but you don't see much around in English. I assume there are political reasons for this.
I come from a Scots family (lots emigrated to Australia in the 1960s) and my grandfather was extremely proud of the little Gaelic he could speak. It pains me that it's been lost in my family.