The A300B4-600 is still in production. This model is quite different from the so-called "classic A300s", i.e. the A300B1, A300B2, and earlier A300B4 versions. For example, Airbus Industries adopted several A310 components for the A300B4-600 (which first flew in the early 1980's), including new materials and the tail section. Furthermore, the A300B4-600 (aka "A300-600") features a modernized two-crew cockpit - whereas earlier A300s had a three-crew cockpit.
Nevertheless, Airbus received only few orders for the A300 in recent years, despite the bestselling A300F4-600 freighter version. In opposite to the variety of A300 freighter operators, only a few took delivery of factory-fresh cargo versions, e.g. FedEx, UPS, Korean Air and CityBird. Most of the others, e.g. MNG Aviation, DHL or TNT, are operating converted pax A300B4s (some of these are converted "classic A300" versions).
Hope this helps,