I'm still searching for my holy grail felt-tip pen which would be a small-nib (.5mm or less?) chisel point (or equivalent.) Any suggestions? Most of the calligraphy markers I've tried aren't suitable for small writing.
Felt tips -> Pilot Parallels -> Flat metal nibs with specific inks.
For large writing, with chisel point width of 1.0 mm or larger, there are many felt-tip pens from at least 4 or 5 manufacturers, and also fountain pens with wide nibs suitable for variable-width lines, e.g. Pilot Parallel pens or Rotring Art pens.
For small writing with variable-width lines caused by nib shape, like you want, I have seen only dip pen nibs, which are inconvenient for casual usage.