Unfortunately, nobody really knows how the Druids decorated themselves, and if by "Pendragons" you mean Arthur and his dad, well, there's no evidence that they ever existed, or used tattoos!  That said, I assume you're thinking of the Celtic-style "armband" tattoos that have been fashionable recently; most of the ones I've seen have been knotwork.  As Kat says, you can find plenty through Yahoo, or indeed pretty well any search engine.  One which has some nice, free clipart is:   Aon Celtic Art

Aidan Meehan has written a series of useful books on Celtic-style design; details of these, and others, from:  The Celtic Art Coracle Online

Malcolm