The A310 and passenger verions of the A300 fall under the odd category of airliners that are no longer actively marketed by the manufacturer, but are available if an airline would place an order.......its a gray area, since airliners are rarely built without an order, so what is the difference? To make it simple, as long as the A300 line is open and producing freighters, Airbus can supply an A310 (or passenger A300, as was done for JAS a few years ago) should an airline really want one. Of course, Airbus would much rather sell an A332 than and A310, but that is another issue.
The best example I can think of is Continentals purchase of 10 762s which they received a couple of years ago.....until CO
's order (part of their 764 deal I believe), a 762 had not come off of the 767 production line for about 4 years I think and Boeing was not actively marketing the type. CO
needed an airliner for long range services that was smaller than the 764, so Boeing built 10 new 762s for Continental with some of new features (including the interior style) of the 764s.