I've set some program listings running and the sound of the ND11 running brings back sooooo many happy memories.
For those of you looking for Nixrdorf ribbons, these ones were listed for an ND10, but fit the ND11 and so should also fit the older and slower ND04 printer as well.
I'm amazed that companies still stock these things and now I know they fit, I'm tempted to buy a few more just in case.
Needless to say, I've now found another supplier in the UK that was half the price of the place I've just used