Oscar and Tony winner Joel Grey literally stumbled onto the West Village pop-up space that he turned into a gallery to celebrate a new book of photographs, “The Billboard Papers.” Grey — who creates his art by “walking around his ’hood, taking art shots,” found the “giant space at Washington and Barrow streets” while taking photos. He inquired about using it for a party, and owner Carla Ruben of Creative Edge Parties said she’d help put together a chic “atelier.” Guests included Agnes Gund, Gay Talese, Ross Bleckner, Bernadette Peters and Isabel and Ruben Toledo. Grey, who starred in “Cabaret,” quipped, “I’ve done a lot in my life . . . but I never thought I’d get a ‘pop-up atelier!’ ”