There's lots in the old oaks in Windsor Great Park, Berks, UK, but, as Liz says, you need a climbing rope to get at it - and watch out for the Duke of E. blasting away with his shotgun. (Is he still head of the Worldwide fund for Nature?)>
RtS (how did Loki make an arrow out of it to kill Baldur or was it only tiped with mistletoe, or have I garbled my Norse mythology)