Rotring Art pen cartridge or converter?

[joolstacho]

I have my ol' dad's Rotring Classic Art Pen, which is close to being a beautiful thing!
It writes beautifully, but starves, perhaps because of the problem below.

The piston ink converter that I have doesn't fit perfectly, just a shade too loose at 6.31mm diameter,
and too long. This means it gets stuck in the tapered body.
I need a piston converter or recommendation for Cartridges.

Can anyone advise or help? Here it is:
https://imagizer.imageshack.com/v2/xq90/924/yLfPA4.jpg (https://imageshack.com/i/poyLfPA4j)

[JayDubya]

I believe the Rotring Art Pen uses short standard international cartridges, like the Kaweco Sport ink cartridges. Kaweco also makes a short converter that should fit. The cartridges can also be easily refilled from bottled ink with a syringe.

[joolstacho]

Thanks for the tip JayDubya, I'll see where I can find them (In Oz it might be more difficult) I do have a cheapo Shaeffer pen which came with some shortish cartridges I'll check them out
No, that didn't work - they're too fat.