I have never heard the term "comic" or "maru", so I had to go looking. Learn something new every day.
I checked out Jet Pens and found a good article describing caligraphy terms and items.
https://www.jetpens.com/blog/guide-to-nibs-and-nib-holders/pt/763
What type of holder do they want, straight or oblique?
For my straight holders use a standard ferrel. It will fit most curve shapped bases, but it won't fit the "maru" which appears to be similar to a crow quill (circular base).
I have made oblique holders, with a bullock flange, that is designed to hold both curve bases and round bases using a screw tightend flange.
Making a straight holder for round based pens (nibs), has its own unique problem. I have been percolating some of my own ideas, but haven't put cutter to lathe yet. l have heard of a maker that did do a crow quill straight holder, but it would not acommodate a curved base pen.
I would be interested to hear what you come up with.