The Folk Directory used to list Hunting the Witches at Pendle in its gazetteer of annual folk customs. However, I can't recall seeing it mentioned in any other book of folk customs, and the Folk Directory used to carry quite a few non-events.

Also, given that the Pendle witch trials did not actually involve any witches (they merely followed patterns of social tension and witchcraft accusation which were extremely common at that time), I'd think it unlikely that there was an annual witchhunting custom which dated back to that period. It's possible of course that someone "invented" such a custom at a later date, perhaps following the publication of Harrison Ainsworth's book. Overall, though, I get the feeling that the whole business is a bit of a cod.

Incidentally, it's many years since I read it, but I recall Edgar Peel and Pat Southern; The Trials of the Lancashire Witches as a pretty good factual account of the episode. For good overviews of witchcraft accusations and their causes, see Alan MacFarlane, Witchcraft in Tudor and Stuart England, and Keith Thomas, Religion and the Decline of Magic.