If you just want the nibs, these should work, Wacom Nibs Standard 10-pack:
Wacom Nibs Standard 10-pack


What I did:
However, the pen didn't feel right in my hand and I found it too tedious to have to select each time with the eraser, so I bought the Lamy AL-star EMR 471.
Lamy AL-star EMR 471 (coated/matte displays)

It's much better and more comfortable in my hand and it's no longer a problem to write for 5 hours at a stretch without my hand hurting afterwards, which I couldn't do before.
It comes with 2 nibs that are a little harder than the original pen, which makes the pencil feel a little less.

What I have done is to buy the Doodroo foil, which is very easy to install, which makes the surface a little smoother and gives more resistance. This way the pencil feeling and sound is even more present than when new. However, the nibs also need a lot more through this way.
https://doodroo.com/products...

Since I didn't want to change the nibs all the time, I ordered titanium nibs, which made it feel like a biro on paper and made it even more direct. I've been using the Boox for three quarters of a year without any problems, there are no scratches and I don't have any more wear material that has to be changed.
https://www.amazon.com/Titanium-C...

Leads only can be found here:
Onyx Box of Boox Pen Tips

E.g. Onyx Pen2Pro