Is there a better refill for Wacom Inkling pen?

I bought a Wacom Inkling Pen and it is a great tool. I’ve been using it a lot and when that happens you start wishing for more. In my case I just want a better ink refill… the one that came with it is a regular ballpoint pen refill 1.0mm (ministar) but I want something darker and smoother to draw. If anyone knows where I can find a better pen refill for it please let me know. I think I search the whole internet and the only refill that google shows is the same ministar 1.0mm pen refill that already came with it. I just want a better line in my drawings, like a gel pen or a darker black ballpoint pen. thanks in advance