Summary

Okay... There are options to buy an original stylus for my Atari CX-77. In US, it costs about US$ 14.00~US$ 15.00, but (thanks to the current communist dictatorial regime here) there are so many taxes to import one to Brazil, that it can cost more than US$ 70,00.
So I decided to 3D print my own version of it.

I modeled the 3 pieces on Blender and printed some tests on "black velvet" PLA.

The body was particularly challenging to print, so I made some later changes and placed it on the OrcaSlicer with the cable side up with automatic tree support, that I also used on the tip piece.
On all 3 pieces I set the seam position as "random" to avoid marks as these pieces are all too small for a 0.4mm printer nozzle.

These photos are from the (0.2b version). This version here already have some minimal modifications, but much probably you will need to make your own adjustments to better fix the cable or the tactile switch.

The measurements of my stylus version certainly do not match the original (and I printed the button as black because I was out of red PLA that time) as I don't have one to make it more close to the original version, but it worked for me (by now).