Kuretake Karappo Pen, Fine Brush tip 5pcs set, Empty refillable ink pen, for lettering, calligraphy, illustration, drawing, Made in Japan

Have you looked at something like these?Each uses about 2ml of ink to fill the core. It would let you use fountain ink in a more accessible way without risking your nice pens. It’s a good way to travel with fountain pen ink too since you don’t need to worry about keeping the pen safe as much. I just filled and tried mine out today and I’ll definitely be adding some to my edc.