ive tried to do the same thing but my area is mostly norse, not celtic. are there any really good lore sources you've been able to find?
Viewing post in thank you for exploring the pagan lore
The best reference for Celtic myth is probably the Mabinogion, although the stories it collects were most likely written down by Christian monks. I mostly google and explore as many different sources as possible because they all have slightly different takes on the material, so I couldn't recommend a single authoritative source. It's always nice to find an obscure retelling that includes some juicy new detail...