I did see some in both scales somewhere recently Ian, but I can't remember who makes them - it might have been Eduard. To be honest, for the relatively short lengths you'd need for gun turrets, you'd be better off making the ammo belts yorself, as the PE ones are 'flat' sheet, just etched to the shape of the rounds, rather than full, 3D, 'tubular' rounds with the links. it's fairly easy, just a bit time consuming, and for an even easier 'fix', where feed chutes or ramps are involved, they can be made by scoring strips of lead foil and painting accordingly. I've done a few this way, and unless you get a magnifying glass and really twist around to see them, especially inside a turret, they look very convincing and acceptable.