Calligraphy could be easily mentioned in the fountain pen section, but we want to emphasise this special form of writing. That’s not only because people still asking for it. It’s because we love writing with expression.
The real big difference between a normal fountain pen and a writing instrument for calligraphy lies in the nip. A feather for calligraphy has no iridium corn at the end of the nip. It is mostly cut off straight at the end. That’s the reason for the varying caption of the line-width, when writing on the paper. The vertical lines are quite broad and the horizontal lines are fine.
Who are looking for a feather like that on a regular fountain pen will have difficulties to find a model with such a nip. If you find one it will have probably a gold-nip and is party of the more expensive collections. Only a few producers, like Lamy and KaWeCo, offer special fountain pens for calligraphy. You get them mostly as a set with multiple nips, so you can change between different nip-sizes.
In case you like it even more traditionally, you will have to look for a quill. Something like that you will find in a specialised shop for art supplies.