Namisu pens use the International Standard Cartridge size in either long or short format (apart form the N1 Pocket Pen which uses short cartridges exclusively):

Converters (Refillable Cartidges)

In the UK you can find these at Cult Pens or any other pen retailer.

In the USA you can find these at Goulet Pens or any other pen retailer. Make sure you filter cartridges to "International Standard" whether short or long.

IMPORTANT: Lamy, Parker, Platinum and other proprietary brands are NOT COMPATIBLE with our pens.