LONDON — Mischa Barton will star in Roland Joffe’s Russian coming-of-age drama “Finding t.A.T.u,” which starts shooting in Moscow later this month.The movie is adapted from the novel “t.A.T.u come back” by Russian writer A. Mitrofanov. Set against a background of music, Internet chatrooms and hedonistic Russian nightlife, it’s the story of a lonely American teenager in Moscow who becomes friends with a local girl over their shared obsession with pop band t.A.T.u. Cast also includes Shantel VanSanten, Anton Yelchin, Alex Kaluzhsky and Helena Mattsson. Producers are Leonid Minkovski and Serge Konov from Mosfilm-based shingle RAMCO, and Stephen Nemeth of Rhino Films. Foresight Unlimited is handling international sales.