You won't find anything because Wicca is not an ancient tradition, what we know as Wicca dates back to the early 20th century (at most to the late 19th century) and it's a practice that was found in a particular part of England, not practiced in other parts of Britain.
"Wicca" and "witchcraft" are not exclusive synonyms rather "witchcraft" is an umbrella term for a multitude of folk practices that were typically distinct to their region and/or culture and often are unrelated to one another. A book that can give you an overview of Wicca's specific history and development is Ronald Hutton's Triumph of the Moon. :)
The best way to find out about your ancestors' possible practices is to delve into your family's genealogy and see who you can identify and what you can learn about them along with learning about the folk customs and history of the regions they were from. That will be research that's primarily in history, literature, archaeology, etc. and not in the New Age/Neopagan sections.
I can't really add much to Callisto's post. The earliest generation in your family to practice Wicca would possibly be a grandparent (if not a great grandparent)...no further back than that. As she said, it's not an ancient religion (few legitimate Wiccans would ever suggest it was). Surely there may be Pagans further back in your family line, but they wouldn't be Wiccan.
Wales had very few witch trials. A book that could help in your research is A History of Magic and Witchcraft in Wales: Cunningmen, Cursing Wells, Witches and Warlocks by Richard Suggett.
I'd recommend reading the Mabinogi to learn about Welsh mythology. The Patrick Ford translation is the one my original HPS recommended to me when I started studying with her coven, before I was initiated. You can find cheaper copies used online.
There are two good sites on the Mabinogi here: