Aangezien een "plunger pen" een soort "fountain pen" is (zie Ref.1)
zou ik het op vulpen houden.
Kroontjespen (met inktcapsule o.i.d.) is een alternatief.

Ref.1 http://www.rickconner.net/penspotters/filling.html
fountain pen filling systems
soort: plunger pens ; plunger fillers
element is de "plunger rod" (inkt reservoir)
...."" Filling
To fill a plunger pen (assuming it's mostly empty), unscrew the blind cap so that it is free of the barrel, then gently pull the plunger rod away from the pen.
With the plunger rod all the way out, immerse the point in an inkwell, then press the plunger rod smartly straight back into the pen.
The pen will expel ink during this downstroke, and draw in new ink at the very end of the downstroke (when a vacuum is broken behind the plunger).
Wait for a ten count, then remove the pen and wipe it down. Screw the blind cap back down to the barrel.
The trick in filling a plunger pen is to make your downstroke as fast as possible (without, of course, bending or breaking the plunger rod).
This will develop the greatest possible vacuum behind the plunger, resulting in a more efficient fill."

Ref.2 http://www.pentrace.com/du_lex.html
Een aardige lexicon voor dit onderwerp

Ref.3 http://www.swisherpens.com/catalog/pelikan/pelikan-toledo-70...
Voorbeeld. "... a classic plunger pen"

Ref.4 http://www.kalligrafie.nl/winkel/N_frame.html?http://www.kal...
Vulpennen