According to Aircraft of the Spanish Civil War by Gerald Howson, the USSR purchased two Breda 64s in 1938, but nothing more is added. One Ba 64 arrived in Spain in 1937 with the Aviazione Legionara from Italy in June 1937 and it received the military serial 8-1, but no more is said about that either - similar info to what Greg has already posted. There is quite a bit of information on the Breda 65 in Spain, a total of 23 were sent and 12 were lost, the Republicans might have shot down either three or six of them - records are conflicting; the 11 survivors entered Ejercito del Aire service after the war ended.