Wicca is the religion which was invented by Gerald Gardner in the 1940s-1950s. It is a product of modern, industrialized, literate civilization. That doesn't mean that Wicca can't provide a field for MudPuppy's sociological research project. Various Wiccan groups may deliberately have decided to let some of their evolving lore remain unwritten. (An analogous case in antiquity is the formation of the Jewish Mishna.) But since Wicca only dates to the 1940s, no Wiccan group can posess "ancient" traditions which have never been written down. Mudpuppy's original posting specifies "ancient" beliefs. In light of what I've posted elsewhere on this thread, MudPuppy's attempt to find "ancient" beliefs will probably prove fruitless if by "ancient" is meant a thousand years old or more. MudPuppy may simply have to relax this qualification and settle for studying oral transmission of more recently formed traditions.
Shamanism is a Siberian practice. "Celtic shamanism" strikes me as an incongruous combination of words. What do you mean by it?