I have a Tropen Gold fountain pen that has a damaged collar & feed. Oxonian assures me that replacement Tropen units are "as rare as rocking horse droppings", so I'll likely have to settle for finding a unit from another manufacturer that happens to fit. I've already tried Pelikan M200 and M400 nib units, but they didn't work. Does anyone know some alternatives that will?? Thanks for any advice you can give,

Don Jr