TOULOUSE, France, Sept 21 (Reuters) - Airbus is in talks with a number of potential customers for a new freighter version of its A350 jetliner, its sales chief said on Tuesday. With e-commerce booming, Airbus formally began marketing the proposed freight variant in July, taking aim at Boeing’s grip on the global cargo market. “We are in a number of very encouraging discussions,” Chief Commercial Officer Christian Scherer told reporters in Toulouse. “It is available for sale and is selling,” he added.