By Amy-Jo Crowley, Oliver Hirt, Andres Gonzalez and Pablo Mayo Cerqueiro LONDON(Reuters) – Swiss stock market operator SIX Group is considering a bid for fund distribution company Allfunds, according to two sources with knowledge of the situation, a move that could be complicated by the difficulty of raising acquisition financing. Allfunds management is expected to meet prospective bidders next month, one of the sources said, while the other said no offer from the Zurich-headquartered SIX was imminent. Amsterdam-listed Allfunds is working with Goldman Sachs and Citigroup on a strategic review …