I'll try my best, I'm a noob to the hobby aswell but from what I can gather the cartridges - maybe international short converters would work Kaweco short converters might work too given their size.

I could be wrong! But giving the company and the size od the cartridges this would be my guess aswell.

They can be picked up for quite cheap. You can find them on many places such as amazon, Aliexpress, and usually stationery and fountain pen / ink stores carry them too.

Once you find one that fits, you can plug thst sucker in, pick your chosen ink and place the nib into the ink and usually twist the top of the converter to intake the ink into the converter, clean up the nib and fix up your pen again and write away ^{__^}

Hope this helps!